Weather Prediction Center (WPC) Home Page

Time 2020-11-19 01:05:25

Web Name: Weather Prediction Center (WPC) Home Page

WebSite: http://www.wpc.ncep.noaa.gov

ID:120515

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Understanding WPC's Excessive Rainfall Risk CategoriesLooking for data from WPC products in a GIS format?View the Winter Storm Severity Index to see potential impacts from winter weather this season North American Surface Analysis Legacy Page:Analyzed at 15Z Tue Nov 17, 2020Analyzed at 18Z Tue Nov 17, 2020Analyzed at 21Z Tue Nov 17, 2020Analyzed at 00Z Wed Nov 18, 2020Analyzed at 03Z Wed Nov 18, 2020Analyzed at 06Z Wed Nov 18, 2020Analyzed at 09Z Wed Nov 18, 2020Analyzed at 12Z Wed Nov 18, 2020Analyzed at 15Z Wed Nov 18, 2020 Surface Fronts and Sea-Level Pressures Legacy Page:Analyzed 15Z Wed Nov 18, 2020Valid 18Z Wed Nov 18, 2020Valid 00Z Thu Nov 19, 2020Valid 06Z Thu Nov 19, 2020Valid 12Z Thu Nov 19, 2020Valid 00Z Fri Nov 20, 2020Valid 12Z Fri Nov 20, 2020Valid 12Z Sat Nov 21, 2020Valid 12Z Sun Nov 22, 2020Valid 12Z Mon Nov 23, 2020Valid 12Z Tue Nov 24, 2020Valid 12Z Wed Nov 25, 2020 ...Warmer than average temperatures expected for the Four Corners statesto the Plains, with chilly temperatures in the East today...The main area of the contiguous U.S. that will see notable precipitationover the next couple of days is California to the Northwest, as a seriesof upper-level disturbances and surface fronts move through the region.Higher elevations of the Cascades, Sierra Nevada, and the NorthernRockies/Sawtooth Mountains/Wind River Mountains can expect 1 to 2 feet ofsnow through Friday morning, and some Winter Storm Warnings and WinterWeather Advisories are in effect. In lower elevations and along the coast,moderate to locally heavy rain is forecast. Additionally, blustery windsare a concern, and Wind Advisories and High Wind Warnings are scatteredthrough parts of the West Coast states toward the Great Basin.Precipitation chances should lessen by the end of the workweek as surfacehigh pressure returns and provide a break for the unsettled West.Elsewhere, generally dry weather is expected across the U.S., though a fewshowers are possible along the east coast of Florida, and some lightrain/snow may occur in the north-central U.S. on Thursday. Given dry,warm, and windy weather in the central U.S., fire danger will be elevatedacross much of the Plains today. High Wind Watches/Warnings are in placefor portions of Wyoming, Red Flag Warnings are in effect for portions ofeastern Colorado, and Wind Advisories are present in Oklahoma and Kansas.Ahead of the upper-level troughing in the Northwest, an upper-level ridgeis forecast over the central U.S. today, which will serve to warmtemperatures to 15 to 30 degrees above normal from the Four Corners statesto the Plains today and stretching toward the Midwest Thursday. Dailyrecord highs for both minimum and maximum temperatures should be scatteredthroughout those areas. Meanwhile along the Eastern Seaboard, a coldsurface high pressure system is in place, and high temperatures areforecast to be below average by 10 to 20 degrees today. This translates tohighs in the 20s for Maine, 30s for the rest of the Northeast, and 40s formuch of the Mid-Atlantic. Farther south, Freeze Warnings and FrostAdvisories are in effect this morning in the Southeast, and Freeze Watchesare in place for eastern portions of the Carolinas stretching intosoutheastern Virginia for Thursday morning. Temperatures should moderateduring the day Thursday and transition to warmer than normal by the end ofthe week as the ridge moves east.TateGraphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php Latest guidance continues to show fairly progressive and broadlycyclonic mean flow aloft. This flow will contain a series ofshortwaves, some of which will be of sufficiently small scaleand/or involve stream interaction uncertainty to lower confidencein important specifics several days out in time. While still notfully resolved, one area of significant precipitation will likelyextend from the central/south-central Plains into the Lower GreatLakes this weekend as a developing wave tracks northeast from thePlains/Middle Mississippi Valley. The other event that appears tohave reasonably good predictability is an increase ofprecipitation over the Pacific Northwest/northern Rockies duringthe first half of next week as stronger flow reaches that region. Shortwave energy reaching the West around late weekend may produceanother area of central/eastern U.S. precipitation next week as itcontinues eastward but with great sensitivity to low-confidencedetails.For the leading central/eastern U.S. evolution from the weekendinto early next week, guidance seems to be in the process oftrying to converge toward a moderately progressive and phasedsolution aloft in contrast to latest CMC runs which still want toshow some flow separation within the overall shortwave--thusholding back a trailing surface wave not depicted in consensus. Recent GFS/GEFS runs have been gradually trending slower with thesurface wave, in the direction of the ECMWF mean that has beenstable over the past couple days (north of Lake Ontario as of 12ZMon). There are still unresolved differences for specifics of thesouthern part of the shortwave with effects onprogression/southward extent of the front trailing from theaforementioned surface wave.The next upper shortwave that reaches the West around Sun andcontinues eastward thereafter also has meaningful timing anddetail differences. Multi-day trends favor the progressivemajority cluster rather than the sharper and slower UKMET as theenergy comes into the West. Farther eastward the guidance hasbeen very inconsistent regarding the strength and timing of theenergy, favoring a conservative blend approach until betterclustering develops.Guidance agrees fairly well that strong upstream flow will reachthe Northwest after Mon but by midweek there are meaningfuldifferences on the exact shape of this flow as well as for detailsdownstream. At that time the 12Z ECMWF more closely resembles thegeneral ideas of the ensemble means than recent GFS/CMC runs.An operational model blend worked well to depict consensus ideasfor about the first half of the period. Then the forecast quicklyincorporated 50-60 percent total weight of the 18Z GEFS/12Z ECMWFmeans while reducing GFS input due to the less favorablecomparison to the means late....Sensible Weather and Hazards...During the weekend expect an area of organized precipitation fromthe central/south-central Plains into parts of the central and/orsoutheastern Great Lakes, as shortwave energy likely encouragessurface wave development through the Middle Mississippi Valley andeastern Great Lakes. Most precip should be in the form of rain,some of which may be locally moderate to heavy, while some snowmay exist in the northern periphery of the moisture shield. Recent trends have nudged the axis of highest rainfall totals abit southward and further adjustments may be possible due todependence on subtle details aloft. Upstream shortwave energyemerging from the West may produce another area of central/easternU.S. precipitation next Mon-Wed but with low confidence inspecifics for timing/coverage/intensity.The general forecast for the Northwest is consistent regarding thetrend toward an increasingly wet pattern as mean troughing aloftover the northeastern Pacific favors onshore flow and theapproach/arrival of surface fronts. Expect highest totals to beover favored terrain across the Pacific Northwest with a secondarymaximum over the northern Rockies, while lighter precipitation mayreach as far south as northern California. Lower levels will seemostly rain and mid-highest elevations of the Coastal ranges,Cascades, and northern Rockies should see snow.Temperatures during the period will vary in accordance with systemprogression. Readings of 5-15F above normal at the start of theperiod on Sat from the southern Rockies into the southerntwo-thirds of the East will get pushed to the south and east aheadof the front anchored by the developing wave forecast to trackinto southeastern Canada by early Mon. Behind the frontmoderately cool air over the West will settle into thecentral/southern Plains through Mon. Less of this cool air willreach the East where readings should only fall to within a fewdegrees on either side of normal after Mon. The Plains should seea warming trend by next Tue-Wed with the northern half of theregion seeing the best chance for some plus 10-15F anomalies forhighs primarily on Wed.RauschAdditional 3-7 Day Hazards information can be found on the WPCmedium range hazards chart at:https://www.wpc.ncep.noaa.gov/threats/threats.phpWPC medium range 500mb heights, surface systems, weather grids,quantitative precipitation, winter weather outlook probabilitiesand heat indices are at:https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gifhttps://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gifhttps://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.htmlhttps://www.wpc.ncep.noaa.gov/qpf/day4-7.shtmlhttps://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4https://www.wpc.ncep.noaa.gov/heat_index.shtml Hawaii Forecast Discussion (Day 1-7)Hawaii Extended Forecast DiscussionNWS Weather Prediction Center College Park MD243 AM EST Wed Nov 18 2020Valid 00Z Thu Nov 19 2020 - 00Z Thu Nov 26 2020Today's guidance continues to agree well on the overall pattern. Trades will trend stronger between now and the weekend as onesurface high passes north of the state around Wednesday night anda stronger high passes by during the weekend. Expect thestrongest winds to be on Sunday. Trades should gradually weakennext Monday-Wednesday as the latter high weakens while trackinginto the eastern Pacific and a trailing front crosses the centralPacific. Over the past day the GFS has trended toward theprevious ECMWF majority cluster in showing rapid departure of anarea of enhanced deep moisture after Wednesday, corresponding tothe weakening/southward movement of a compact upper low initiallyjust southwest of Kauai. After this moisture departs expectprecipitable water values to fluctuate for the rest of the perioddepending on pockets of moisture carried along in the trades. There is a general signal among the models/means that PWATs may belowest late weekend into early next week. Showers will favorwindward and mountain areas but may occasionally stray to otherlocations.Rausch Additional Links Valid 12Z 11/20/2020 - 12Z 11/21/2020Valid 00Z 11/22/2020 - 00Z 11/23/2020Valid 00Z 11/23/2020 - 00Z 11/24/2020Valid 00Z 11/24/2020 - 00Z 11/25/2020Valid 00Z 11/25/2020 - 00Z 11/26/2020 Valid 12Z 11/18/2020 - 12Z 11/20/2020 Valid 12Z 11/18/2020 - 12Z 11/21/2020 Valid 12Z 11/18/2020 - 12Z 11/23/2020 Valid 12Z 11/18/2020 - 12Z 11/25/2020Valid 12Z 11/18/2020 - 00Z 11/19/2020Valid 18Z 11/18/2020 - 06Z 11/19/2020Valid 00Z 11/19/2020 - 12Z 11/19/2020Valid 06Z 11/19/2020 - 18Z 11/19/2020Valid 12Z 11/19/2020 - 00Z 11/20/2020Valid 18Z 11/19/2020 - 06Z 11/20/2020Valid 00Z 11/20/2020 - 12Z 11/20/2020Valid 06Z 11/20/2020 - 18Z 11/20/2020Valid 12Z 11/20/2020 - 00Z 11/21/2020Valid 18Z 11/20/2020 - 06Z 11/21/2020Valid 00Z 11/21/2020 - 12Z 11/21/2020Excessive Rainfall Forecasts Legacy Page:Valid 16Z Wed Nov 18 2020 - 12Z Thu Nov 19 2020Valid 12Z Thu Nov 19 2020 - 12Z Fri Nov 20 2020Valid 12Z Fri Nov 20 2020 - 12Z Sat Nov 21 2020 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHERN CALIFORNIA AND SOUTHWEST OREGON...1600 UTC updateNo changes made to the previous Excessive Rainfall Outlook.Oravec0900 UTC discussionContinued onshore upslope flow and additional shortwaves moving into the region will result in a persistence of showers today into tonight across western WA/OR into northern CA. The post frontal environment will result in generally decreasing PWs though the day...however cooling temperatures aloft will support the development of weak instability. Given the post frontal environment activity should be more showery in nature, with the weak instability supporting localized 0.5" an hour rains (although the majority of time rates should stay below 0.5"). One shortwave around 12z this morning, and another moving ashore tonight should help focus some briefly heavier rains as well. All in all it seems like a pretty low flood risk given the showery precip nature, low PWs, and ability for this region to handle heavy rainfall. With that said, we are looking at additional rains of 2-3" over the coastal ranges of southwest OR and northwest CA, which is on top of the 4-7" that has fallen over the past 72 hours. Thus possible that some localized minor flood issues do evolve across this area, and will maintain the Marginal risk. The Marginal risk over the western slopes of the Sierra was maintained as well, as this includes the Bear and Claremont fire areas within the North Complex burn scar, where rainfall rates/totals may be enough to result in localized flash flooding.Chenard Day 1 threat area: Excessive Rainfall DiscussionNWS Weather Prediction Center College Park MD246 AM EST Wed Nov 18 2020 Day 2Valid 12Z Thu Nov 19 2020 - 12Z Fri Nov 20 2020 The probability of rainfall exceeding flash flood guidance is less than 5 percent.Hayes Day 2 threat area: Excessive Rainfall DiscussionNWS Weather Prediction Center College Park MD247 AM EST Wed Nov 18 2020 Day 3Valid 12Z Thu Nov 19 2020 - 12Z Fri Nov 20 2020 The probability of rainfall exceeding flash flood guidance is less than 5 percent.Hayes Day 3 threat area: Additional LinksProbabilistic Heavy Snow and Icing DiscussionNWS Weather Prediction Center College Park MD350 AM EST Wed Nov 18 2020Valid 12Z Wed Nov 18 2020 - 12Z Sat Nov 21 2020Days 1-3......Western U.S....No major changes to the previous thinking. A broad upper troughmoving over the western U.S. over the next few days will continueto foster a weakly cyclonic upper-level flow pattern. Multipleembedded shortwaves in this deeper layer flow and associated wavesof low pressure will help to maintain a fetch of mid-level Pacificmoisture across the Intermountain Region going through at leastThursday. The combination of larger-scale forcing associated withthe shortwave energy and the moist, upslope flow into the west andsouthwest facing slopes of the higher terrain should maintain athreat for heavy accumulating snowfall as a result. By Friday, theGreat Basin will begin to dry out as high pressure builds over theregion, but there will be some shortwave energy/troughingapproaching the central Rockies, and also still a fetch of Pacificmoisture still impacting portions of western WA that will maintaina threat of some wintry weather precipitation for the higherterrain.More specifically, the next shortwave impulse will advance onshorethe OR/WA coast early this morning accompanied by rather strongupper-level divergence associated with the LFQ of the upper-leveljet-streak nosing into the region. This will spread snowfallacross many of the ranges from the Olympics of WA, southwardthrough the northern Sierra Nevada, and as far east as the Tetonsof WY. Snow levels will gradually fall going through today andtonight, with snow levels falling to as low as 2000 to 3000 feetfarther north in the WA Cascades, and down to perhaps as low as5000 to 6000 feet in the Sierra-Nevada. Snow levels will be a bithigher farther east over the northern Rockies and generally in the6000 to 7000 feet range. A second shortwave impulse will arrive onThursday with additional height falls and forcing associated withthis which will yield a second round of locally heavy accumulatingsnowfall. The combination of these two shortwave impulse isexpected to foster additional snowfall totals going through earlyFriday of as much as 1 to 2 feet, with the heaviest accumulationsover the WA Cascades and also locally over the southwest facingslopes of the Sawtooth where some isolated additional amounts over2 feet will be possible. Consequently, there are some locallyelevated WPC snowfall probabilities for exceeding 12 inches ofsnow over these areas.On Friday and through early Saturday, a moist Pacific fetch willstill be impacting portions of the WA Cascades which may yield anadditional 6 to 12 inches for this period here, but with highersnow levels. Elsewhere, expect locally several inches of snow tobe possible over the central Rockies, and especially northern COas shortwave energy attempts to amplify toward this region.For Days 1-3, the probability of significant icing (0.25-inch ormore) is less than 10 percent. Orrison Additional LinksValid 12Z Sat Nov 21, 2020Valid 12Z Sun Nov 22, 2020Valid 12Z Mon Nov 23, 2020Valid 12Z Tue Nov 24, 2020Valid 12Z Wed Nov 25, 2020 Latest guidance continues to show fairly progressive and broadlycyclonic mean flow aloft. This flow will contain a series ofshortwaves, some of which will be of sufficiently small scaleand/or involve stream interaction uncertainty to lower confidencein important specifics several days out in time. While still notfully resolved, one area of significant precipitation will likelyextend from the central/south-central Plains into the Lower GreatLakes this weekend as a developing wave tracks northeast from thePlains/Middle Mississippi Valley. The other event that appears tohave reasonably good predictability is an increase ofprecipitation over the Pacific Northwest/northern Rockies duringthe first half of next week as stronger flow reaches that region. Shortwave energy reaching the West around late weekend may produceanother area of central/eastern U.S. precipitation next week as itcontinues eastward but with great sensitivity to low-confidencedetails.For the leading central/eastern U.S. evolution from the weekendinto early next week, guidance seems to be in the process oftrying to converge toward a moderately progressive and phasedsolution aloft in contrast to latest CMC runs which still want toshow some flow separation within the overall shortwave--thusholding back a trailing surface wave not depicted in consensus. Recent GFS/GEFS runs have been gradually trending slower with thesurface wave, in the direction of the ECMWF mean that has beenstable over the past couple days (north of Lake Ontario as of 12ZMon). There are still unresolved differences for specifics of thesouthern part of the shortwave with effects onprogression/southward extent of the front trailing from theaforementioned surface wave.The next upper shortwave that reaches the West around Sun andcontinues eastward thereafter also has meaningful timing anddetail differences. Multi-day trends favor the progressivemajority cluster rather than the sharper and slower UKMET as theenergy comes into the West. Farther eastward the guidance hasbeen very inconsistent regarding the strength and timing of theenergy, favoring a conservative blend approach until betterclustering develops.Guidance agrees fairly well that strong upstream flow will reachthe Northwest after Mon but by midweek there are meaningfuldifferences on the exact shape of this flow as well as for detailsdownstream. At that time the 12Z ECMWF more closely resembles thegeneral ideas of the ensemble means than recent GFS/CMC runs.An operational model blend worked well to depict consensus ideasfor about the first half of the period. Then the forecast quicklyincorporated 50-60 percent total weight of the 18Z GEFS/12Z ECMWFmeans while reducing GFS input due to the less favorablecomparison to the means late....Sensible Weather and Hazards...During the weekend expect an area of organized precipitation fromthe central/south-central Plains into parts of the central and/orsoutheastern Great Lakes, as shortwave energy likely encouragessurface wave development through the Middle Mississippi Valley andeastern Great Lakes. Most precip should be in the form of rain,some of which may be locally moderate to heavy, while some snowmay exist in the northern periphery of the moisture shield. Recent trends have nudged the axis of highest rainfall totals abit southward and further adjustments may be possible due todependence on subtle details aloft. Upstream shortwave energyemerging from the West may produce another area of central/easternU.S. precipitation next Mon-Wed but with low confidence inspecifics for timing/coverage/intensity.The general forecast for the Northwest is consistent regarding thetrend toward an increasingly wet pattern as mean troughing aloftover the northeastern Pacific favors onshore flow and theapproach/arrival of surface fronts. Expect highest totals to beover favored terrain across the Pacific Northwest with a secondarymaximum over the northern Rockies, while lighter precipitation mayreach as far south as northern California. Lower levels will seemostly rain and mid-highest elevations of the Coastal ranges,Cascades, and northern Rockies should see snow.Temperatures during the period will vary in accordance with systemprogression. Readings of 5-15F above normal at the start of theperiod on Sat from the southern Rockies into the southerntwo-thirds of the East will get pushed to the south and east aheadof the front anchored by the developing wave forecast to trackinto southeastern Canada by early Mon. Behind the frontmoderately cool air over the West will settle into thecentral/southern Plains through Mon. Less of this cool air willreach the East where readings should only fall to within a fewdegrees on either side of normal after Mon. The Plains should seea warming trend by next Tue-Wed with the northern half of theregion seeing the best chance for some plus 10-15F anomalies forhighs primarily on Wed.RauschAdditional 3-7 Day Hazards information can be found on the WPCmedium range hazards chart at:https://www.wpc.ncep.noaa.gov/threats/threats.phpWPC medium range 500mb heights, surface systems, weather grids,quantitative precipitation, winter weather outlook probabilitiesand heat indices are at:https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gifhttps://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gifhttps://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.htmlhttps://www.wpc.ncep.noaa.gov/qpf/day4-7.shtmlhttps://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4https://www.wpc.ncep.noaa.gov/heat_index.shtml Additional Links These tools are NOT operationally supported. Data may not update regularly due to workstation failure and/or data unavailability. 1/3/6/24-hr Changes Change in weather parameters (temperature, dewpoint, surface pressure, etc) over the last 1/3/6/24 hours. Data is provided from the Real-Time Mesoscale Analysis (RTMA) or the Rapid Refresh (RAP). GEFS Probabilities Plots of GEFS probabilistic forecast of precipitation, temperature, and sea-level pressure exceeding various thresholds. Local Storm Reports Custom plots of Local Storm Reports across the Contiguous United States. Reports include rain, snow, ice, and severe weather, as well as other significant information from storm spotters. Experimental Extreme Precipitation Monitor Displays the climatological significance of precipitation forecast by WPC. The climatological significance is represented by Average Recurrence Intervals (ARIs) of precipitation estimates from NOAA Atlas-14 and Atlas2. Ensemble Situational Awareness Table An interactive situational awareness table that displays anomalies, percentiles, and return intervals from the GEFS, NAEFS, and ECMWF Ensembles (login required to view ECMWF data). *Please note that there is currently an issue where only users on a NOAA network can access this page. We are actively working to resolve this problem. NDFD Forecast Temperature Records Interactive display of where temperatures could approach or exceed records within the contiguous U.S. (based on NDFD temperature forecasts) NWS NDFD Max/Min Temperatures and Departure from Normal Displays Days 1-7 NDFD maximum and minimum temperatures, along with their respective departures from climatology. Prototype Snowband Probability Forecasts An interactive tool that depicts areas of heavy snowfall from individual members of high-resolution short range ensemble forecasts. Weather in Context Prototype Displays forecast information and its climatological context to quickly alert a forecaster when a record or neear-record breaking event is possible. This tool is available for both CONUS and Alaska. CIPS Guidance Analog guidance that uses an objective approach to find historical events that are similar to the upcoming forecast. National Blend of Models Nationally consistent and skillful suite of calibrated forecast guidance based on a blend of both NWS and non-NWS numerical weather prediction model data and post-processed model guidance. Atmospheric River Portal A portal for atmospheric river forecasts and diagnostics from the GEFS. GEFS Plumes An interactive display of time series plots from GEFS ensemble members at a point. SPC Forecast Tools A variety of useful tools generated at The Storm Prediction Center (SPC). ECMWF Ensemble Mean and Spread Output from the ECMWF 'Ensemble Prediction System' (ENS) for four parameters: mean sea level pressure, 850 hPa temperature, 850 hPa wind speed, and 500 hPa geopotential height. GFS/FV3 Comparison Page An interactive comparison of the GFS and FV3.

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