Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/30/20

Area Forecast Discussion
National Weather Service La Crosse WI
558 PM CST Tue Dec 29 2020 .SHORT TERM...(This evening through Wednesday Morning) Issued at 247 PM CST Tue Dec 29 2020 At 1930Z, snow was spreading into the area with a quick drop to 1 mile or less visibility in most places. The forecast continues to be on track...with a minor adjustment down in the snow totals from this morning...about 1 inch. Intense moisture surge of over 200% normal precipitable water now has its leading edge around I-80 in Iowa. This is reflected by higher reflectivity echo and will shift just south of the forecast area. This is transitioning to heavy snow as it moves north and its track, or northern extent, is just south of previous forecasts. The northern side of this schield should track into the warning area, but the CAMS and 29.12Z SPC HREF target higher 1-2"/hr snow rate probabilities slightly south of the forecast area. As Bob Uecker says, "Just a bit outside". But, the northern extent will certainly have influence to reach warning snows. When this area hits locally, it will really snow heavy for the 5-9 pm window. 280K isentropic surface is beautiful today via the RAP and really provides a nice visual of the upglide, moisture plume, 40-50kt winds in the 800-900 mb layer - as well as the sharp north-south boundary shifting to subsidence. Also evident is the sharper back edge to the precipitation axis in eastern SD/NE. This will continue to shift east and end precipitation earlier across MN than previously thought. Thus, have lowered snow amounts some in that area. With the major moist plume shifting to just south of the area, have also lowered amounts on the NW edge of the warning...but only by an inch. Overall, have decided to end the Warnings and Advisories 3 hours earlier based on the increase in speed. The bulk of accumulations should be done by midnight. Travel conditions should be improving rapidly Wednesday morning. .LONG TERM...(Wednesday night through Tuesday) Issued at 247 PM CST Tue Dec 29 2020 Wednesday afternoon into Thursday...system exits to the east of the forecast area and surface ridge builds into central Wisconsin and eastern Iowa by 12z Thursday. Drier air advects into the forecast area and skies will clear from west to east Wednesday night...providing mostly sunny skies and near normal temperatures Thursday. Focus then turns to late Thursday night into New Year`s day. The 29.12z GFS/ECMWF/NAM in decent agreement in lifting upper level low over the Southern Plain States into the Great Lakes Region New Year`s Day. The main difference is the NAM is further north with surface low...hence advects warmer air further north into the southern forecast area. However...the latest 29.12z GEFS members suggest the NAM to be an outlier and will follow more the 29.12z GFS/ECMWF/GEFS track. This will keep the wintry mix across the far southern part of the forecast area. Ice accumulation at this time look to be up to a tenth of an inch and snow amounts up to 2 inches. Main forecast concerns Saturday through Tuesday are temperatures through the period. The 29.12z GFS/ECMWF/GEM are in good agreement in developing west to east zonal flow across the continental United States through the period. The deterministic models suggest weak impulses embedded in flow aloft to track across the northern tier states through period. However...forcing/lift is weak with each piece of energy and looks to be mainly dry through the period. Temperatures through period will be above the deterministic models indicate 925mb minus 2 to plus 3 degrees celsius and the 29.12z NAEFS show temperatures plus 1 to near plus 2 standard anomalies at 850mb by Monday and Tuesday. Expect high temperatures to be in the lower to middle 30s Monday and Tuesday across forecast area. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 558 PM CST Tue Dec 29 2020 MVFR to IFR conditions are expected into tonight, with snow tapering off from west to east over the next few hours. There may be a couple of hours of fog or very light freezing drizzle behind the snow, but conditions should improve later tonight as the low pressure system pushes east. Guidance does suggest lower ceilings eventually sneak in from the west, and have brought IFR ceilings into KRST later tonight as a result. Ceiling and visibility trends will have to be monitored for possible adjustments, however. Low level moisture looks to stick around through much of Wednesday, so confidence is low on whether low clouds will be able to clear out during the day. Winds will turn from southeast to westerly tonight, with gusts near 20 kts possible early this evening and again Wednesday. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Storm Warning until 9 AM CST Wednesday for WIZ053>055-061. Winter Weather Advisory until 9 AM CST Wednesday for WIZ017-029- 034-042>044. Winter Weather Advisory until 6 AM CST Wednesday for WIZ032-033- 041. MN...Winter Weather Advisory until 6 AM CST Wednesday for MNZ079- 086>088-094>096. IA...Winter Storm Warning until 9 AM CST Wednesday for IAZ009>011-018- 019-029-030. Winter Weather Advisory until 6 AM CST Wednesday for IAZ008. && $$ SHORT TERM...Baumgardt LONG TERM...DTJ AVIATION...Lee
Area Forecast Discussion
National Weather Service Buffalo NY
1002 PM EST Tue Dec 29 2020 .SYNOPSIS... High pressure ridge from New York to the North Carolina coast will provide dry weather most of the overnight. A warm front will move through the area Wednesday morning with a chance of some light snow possibly mixed with sleet. The warm front will usher in warmer temperatures for Wednesday afternoon, with an approaching cold front then bringing a period of rain showers late Wednesday and Wednesday night. The rain may be mixed with or take form of a wintry mix especially in the interior Southern Tier and east of Lake Ontario. Any rain will then end as some wet snow and lake effect snow showers Wednesday night into Thursday. && .NEAR TERM /THROUGH WEDNESDAY/... Still have some lake effect clouds off southeast Lake Ontario and to east of Lake Erie with just thin high clouds streaming in over all but North Country. Clear and calm conditions east of Lake Ontario to St. Lawrence and temps have plummeted to near zero there, so lowered mins there for the rest of the night. Temps elsewhere will stabilize and even rise slightly as clouds thicken from west ahead of warm front aloft that moves in toward daybreak. Warm front aloft traverses the Lower Lakes Wednesday morning. Brief saturation occurs especially over Niagara Frontier and across Southern Ontario/western Lake Ontario. Seems that only looking at a hundredth or two of QPF per HRRR which is matching upstream radar trends to this time. Point soundings for this leading edge of precip indicate snow or maybe some sleet as it ends. Given very dry layer seen on BUF sounding this evening, would expect good wet bulb cooling and trended forecast toward ptype of snow with a chance of sleet through mid morning. Will become breezy and warmer in wake of this morning precip and ahead of sfc cold front that approaches in the afternoon. Expect highs to reach the low to mid 40s along the Lake Plains in the afternoon. By that time, more widespread precip is expected to move in from the west as upper trough and associated sfc low and cold front slide across lower Great Lakes. Though most areas will see only rain as ptype in the afternoon, colder air will be harder to displace from the interior Southern Tier as well just inland across the North Country. There are differences in models in just how warm the warm layer aloft around H85/5kft AGL becomes, with the NAM/GFS still warmest and Canadian coldest. Where temps stay cold in the interior Southern Tier could see rain/sleet or even freezing rain. Seems the better chance of more frozen precip in form of sleet and snow will be across the North Country. Greatest confidence in seeing enough snow/sleet to cause some issues will be over the North Country as seen in latest HRRR output as well with at least a couple inches of snow/sleet, but this is very late on Wednesday. Meanwhile due to questions with warm layer/ptype, there is lesser confidence in seeing only freezing rain over interior Southern Tier. Overall at this point, put a mention in HWO of possible wintry mix both of these areas, but given uncertainty opted for no advisory headlines. Mid shift can take another look at this with new guidance to see if advisory will be needed. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... The cold front shifts through Wednesday night. With its passage, west-northwest flow drops 850 hPa temperatures enough to start to get a lake response. This is reflected well in the Canadian, so the forecast was pushed largely toward that guidance through Thursday. However, as large scale moisture departs, lake effect will not have the gusto that it has had recently. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Low pressure over the lower Mississippi Valley will return the cold front as a warm front, which will slowly work its way across the area on Friday. Some light snow may develop out ahead of the warm front as it approaches from the south Friday morning. As the warmer air aloft noses into the area, model soundings indicate a better sustained shallow surface freezing layer on the higher terrain in the Southern Tier and the Tug Hill Plateau. This may facilitate the formation of freezing rain Friday afternoon for the Southern Tier and later Friday evening for the Tug Hill, though there still remains uncertainty with timing and duration this far out. The area should see all rain by Friday evening, which will gradually taper off through the day Saturday. A Southern Stream shortwave trough trails behind the low pressure system, passing to our south during the day Sunday. 12z model guidance has hinted at this shortwave possibly phasing with a northern stream longwave trough, which could nudge it far enough north to bring another round of precip for the area. High pressure builds in as this system passes to our southeast, bringing dry weather through Tuesday. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Westerly flow will support a few lake effect clouds east and southeast of Lake Erie and Lake Ontario through midnight. Dry weather will prevail with VFR conditions. On Wednesday, CIGS and VSBY will remain VFR until late in the day with approaching cold front. Expect LLWS to develop at all TAF sites in the morning with gusty sfc winds over 25 knots following in the afternoon. A chance of light snow, mixed with sleet in the morning will be followed by mainly rain mid to late afternoon. However, there could be a wintry mix over the interior Southern Tier in the afternoon and east of Lake Ontario late Wednesday into Wednesday evening. CIGS will eventually trend MVFR by late day. Best chance of IFR or MVFR VSBY late on Wednesday will be east of Lake Ontario where ptype may stay mainly snow. Outlook... Wednesday night and Thursday morning...MVFR/IFR with rain likely, possibly ending as wet snow. Improvement to VFR Thursday afternoon. LLWS possible Wednesday night. Friday...IFR/MVFR with rain likely. Possibly starting as a wintry mix at onset. Saturday...MVFR with chance of snow. Sunday...MVFR with a chance of rain and snow showers. && .MARINE... Southerly winds will rapidly increase Wednesday ahead of a cold front, producing another round of Small Craft Advisory conditions for the eastern Great Lakes, which will then last into Thursday. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory from 10 AM Wednesday to 7 AM EST Thursday for LEZ040-041. Small Craft Advisory from 1 PM Wednesday to 1 PM EST Thursday for LOZ042-043. Small Craft Advisory from 10 AM Wednesday to 7 PM EST Thursday for LOZ044-045. && $$ SYNOPSIS...Fries/Hitchcock/JLA NEAR TERM...Fries/JLA SHORT TERM...Fries LONG TERM...PP AVIATION...Fries/JLA MARINE...Fries/Hitchcock/JLA
Area Forecast Discussion
National Weather Service Corpus Christi TX
545 PM CST Tue Dec 29 2020 .AVIATION /00Z TAFs/ ... VFR conditions are currently prevailing across all terminals with the exception of VCT. Isolated showers will continue to impact the Victoria Crossroads this evening. Brief MVFR/IFR conditions can be expected with any passing shower. Ceilings will lower to MVFR levels overnight as low level stratus builds back in. Gusty southeasterly winds will weaken slightly tonight before restrengthening by mid day tomorrow with gusts from 25-30 knots possible across the eastern 3 terminals. VFR conditions are expected to return by mid morning. Included a mention of VCSH at CRP and VCT tomorrow as isolated showers are possible during the day. Chances for showers and storms will increase just beyond this TAF window as a cold front nears the region. && .PREV DISCUSSION... /Issued 348 PM CST Tue Dec 29 2020/ SHORT TERM (Tonight through Wednesday Night)... Rich moisture continued to overspread the region this afternoon on very breezy southeasterly winds. Satellite and RAP mesoanalysis reveal a moist axis extending from the western Gulf NNW to the Victoria Crossroads coincident with a band of low-topped showers. Even though a 45-50 knot southerly LLJ develops tonight over the Coastal Plains, additional moisture advection from this jet appears negligible given its drier continental source region. However, a broad stratus shield should still develop overnight which combined with breezy SE winds will keep lows much milder than recent nights. PWATs on Wednesday rise to between 1 and 1.3 inches from west to east as winds aloft back more southerly ahead of a vigorous upper low crossing northern Mexico. Throughout much of the daytime Wednesday, background ascent appears rather muted with only some showers and a few thunderstorms at times. This picture should completely change by Wednesday night as significant forcing arrives - not with just a strong cold front but also large height falls, a 120 knot upper jet, and favorable upper diffluence east of the approaching upper low. Models and CAMs agree nicely with the strongest ascent occurring generally from 10 PM until just before daybreak Thursday. An axis of MLCAPEs of 1000-1300 J/kg along the Coastal Bend north to the Crossroads will be the focus for some brief severe modes as the cold front drops south, although this threat may take a back seat to heavy rain/minor flooding given PWATs of 1/2 to 3/4 inch above normal, deep southerly flow and cell training modes evident on various CAMs. Latest QPF from the HREF mean depicts a core of 2-3 inches across the Victoria Crossroads which could still cause some flooding concerns despite rather dry soils. LONG TERM (Thursday through Tuesday)... Rain and thunderstorm chances are expected to linger into Thursday morning across South Texas, before drying out in the afternoon as moisture decreases behind the front and the upper level low exits the region to our north. At this time, a warm thermodynamic profile continues to support rainfall as the primary precip type across the area on Thursday, with the frozen precip remaining farther north over the Texas Hill Country. However, if the upper low shifts slightly southward than anticipated, then can`t rule out brief isolated sleet or graupel across the northern Rio Grande Plains and Brush Country. But, little to no impacts are expected if that were to occur due to the warm surface temperatures and quick melting. Breezy to windy conditions can also be expected behind the front on Thursday which may approach Advisory criteria by Thursday afternoon. In addition to the gusty winds, expect much cooler temperatures in the wake of the front on Thursday, with highs struggling to get out of the 50s due to the thick cloud cover and the arrival of CAA. New Year`s Eve looks much drier and calmer as PWATs are progged to drop to below a half an inch, with a clearing in the cloud cover expected to occur from southwest to northeast. The combination of the clear skies, lighter winds and a much drier and cooler mass in place will allow for optimal radiational cooling to occur by New Year`s morning, with the lows forecast to fall into the 30s across most of the area. A light freeze will be possible over portions of the Coastal Plains, but it`s not anticipated to be widespread and rather more localized over low-lying and drainage areas. These dry and cooler conditions are expected to persist through most of the weekend, with the exception of a few spotty showers here and there with the arrival of a couple of weak disturbances in the mid/upper flow. Winds will become onshore on Sunday leading to a gradual warm- up and moisture increase through early next week. Rain chances may return late in the period with the arrival of deeper moisture and a coastal trough. MARINE... Moderate to strong southeasterly flow continues tonight through the day on Wednesday. A Small Craft Advisory remains in effect through Wednesday evening, and may continue through Wednesday night ahead of a strong cold front. Following isolated to scattered showers tonight along with a few thunderstorms on Wednesday, numerous showers and thunderstorms are expected Wednesday night ahead of the front. The cold front is expected to move across the coastal waters Thursday morning with the winds shifting to the west and strengthening through the day. Strong to very strong offshore flow with frequent gusts to gale force is expected to develop by Thursday afternoon and continue Thursday night. The offshore flow will diminish Friday with weak to moderate north winds expected by Friday afternoon and continuing through Saturday night. A weak to moderate onshore flow will resume Sunday afternoon into Sunday night. Showers and thunderstorms will begin to diminish by Thursday afternoon. Isolated showers will be possible again Friday night. && .PRELIMINARY POINT TEMPS/POPS... Corpus Christi 65 80 51 60 39 / 20 40 100 50 0 Victoria 64 78 51 59 37 / 40 50 100 80 0 Laredo 62 80 43 56 38 / 0 10 80 30 0 Alice 64 83 48 58 37 / 20 30 100 50 0 Rockport 67 76 52 61 42 / 30 40 100 70 0 Cotulla 62 78 43 50 34 / 10 20 100 50 0 Kingsville 64 83 49 59 37 / 20 30 100 50 0 Navy Corpus 68 78 52 61 45 / 20 40 100 60 0 && .CRP WATCHES/WARNINGS/ADVISORIES... TX...None. GM...Small Craft Advisory until 6 PM CST Wednesday For the following zones: Bays and Waterways from Baffin Bay to Port Aransas... Bays and Waterways from Port Aransas to Port O`Connor... Coastal waters from Baffin Bay to Port Aransas out 20 NM... Coastal waters from Port Aransas to Matagorda Ship Channel out 20 NM...Waters from Baffin Bay to Port Aransas from 20 to 60 NM...Waters from Port Aransas to Matagorda Ship Channel from 20 to 60 NM. && $$ TC/95...AVIATION
Area Forecast Discussion
National Weather Service Des Moines IA
553 PM CST Tue Dec 29 2020 ...Updated Aviation Discussion... .DISCUSSION.../Tonight through Tuesday/ Issued at 301 PM CST Tue Dec 29 2020 Forecast Highlights: -- Ongoing winter storm having significant impact on travel, especially over central and southern Iowa. -- High snow rates have led to rapid accumulation in some areas -- Transition to wintry mix in the south is ongoing and will continue into this evening -- Late week wintry precipitation still on track Details: GOES-East upper level water vapor shows the plume of moisture ahead of the shortwave trough that has ejected out of the base of the western US longwave trough. Sporadic and embedded lightning has occurred with the precipitation shield, especially over Kansas into northern Missouri earlier this morning and more recently in Adams County within the last 30 minutes. QPF has been raised to the 75th percentile of guidance, which helped to up QPF amounts in a narrow band from Taylor/Ringgold Counties up toward Warren/Lucas and Poweshiek/Mahaska. This is a trend noted in the 12z guidance from HREF, HRRR, and RAP. This along with negative EPV and steep mid- level lapse rates noted on area soundings in HRRR and RAP guidance will lead to continued chances of thunder- wintry precipitation, which will locally enhance rates. 12z HREF guidance is all in on greater than 1"/hr rates from Des Moines/Polk County and surrounding counties mid-afternoon moving east-northeastward into this evening and over east central Iowa/Dubuque area. The highest probabilities and even some less than 40% probabilities of 2"/hr rates are over east central Iowa and that is where WFO Quad Cities has amounts around double digits. Given incoming reports this afternoon, the 1"/hr rates are more than verifying and probably in some cases approaching 2"/hr. With these high snow rates making it challenging for road crews, worst impacts will be into at least early this evening and lingering longer as lighter precipitation continues. Farther south, spotter reports as well as observational trends in surface and radar data have shown a changeover to sleet or freezing rain as the warm nose aloft moves over southern Iowa. KMCI had around 0.15" of ice so far with freezing rain and sleet across northern Missouri according to our neighboring office WFO Pleasant Hill/Kansas City. Thus, have tried to increase freezing rain in the far south. NBM 50th percentile supportive of amounts to around that value or a bit higher. Some deterministic output is quite high with freezing rain amounts, but there is uncertainty in accretion given high rate of rainfall. A recent spotter report from Murray indicated heavy freezing rain keeping concerns of accretion a concern going into the rest of this afternoon. Farther north where there is the transition to sleet, this will hamper snow amounts with a tricky transition zone likely near or south of the I-80 corridor, especially east of Des Moines. At this point, no change in headlines given the wintry mix bag the south has had with predominately snow north of Highway 30. As drier mid-level air works in as the precipitation begins to depart this evening, there is the possibility of a little freezing drizzle. Amounts will be light from a glaze to perhaps a few hundredths. By daybreak Wednesday, the precipitation will be over for central Iowa, though roadway impacts will linger. The next weather system to impact our area will be late this week/next year. A shortwave trough that is digging over the Southern California coast this afternoon into the base of the longwave trough will translate across northern Mexico and then lift northward quickly late this week. Surface low pressure will passes southeast of the state with Gulf of Mexico moisture being pulled back into the deformation zone. This will yield a mainly snow event for areas farther northwest in the state while a wintry mix may occur over southeastern sections of the state. The most likely area for wintry precipitation will be over southeast Iowa into central Iowa with chances tapering to nothing over far northwest Iowa. && .AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/ Issued at 543 PM CST Tue Dec 29 2020 Heavy snow band mixed with some freezing drizzle and even sleet looks to mainly impact DSM, OTM and ALO this evening. Still looking at IFR ceilings for much of the night into early Wednesday morning before gradually lifting to MVFR overnight and then with the CAA developing anticipating ceilings to lift to VFR late in the TAF period. && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 6 AM CST Wednesday for IAZ017-025>028- 034>039-044>050-057>062-070>075-081>086-092>097. Winter Weather Advisory until 6 AM CST Wednesday for IAZ004>007- 015-016-023-024-033. && $$ DISCUSSION...Ansorge AVIATION...Podrazik
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
830 PM EST Tue Dec 29 2020 .UPDATE... Amplified upper level ridge axis over the Central Great Lakes early this evening, as 00z DTX Raob checks in with 560 DAM height at 500 MB, close to the 90th percentile based on climatology. The sounding also revealed some very dry low levels, as 700 MB dew pt comes in at -38 C. Consolidating northern stream upper level PV/main mid level circulation over the Dakotas, which will be tracking across Lake Superior Tomorrow. Main forcing will be associated with the nose of a strong low-mid level jet (65-75 knots) over the Midwest which will veering a bit tonight and tracking through Lower Michigan early tomorrow morning, allowing for an excellent surge of moisture (specific humidity 4.5+ g/kg) to overcome the dry low levels. The inherited forecast looks to be in good shape as far as I can tell, with the narrow warm advection arm lifting through late this evening/around midnight. Best forcing up around 600 MB, where temps reside in the negative lower teens. The strong, but short lived forcing lifts north overnight, leading to lull for southern two thirds of the CWA. The track of the low level jet and continued isentropic ascent likely helps maintain snow across Tri-Cities region and northern Thumb region. A 1-3 inch snowfall generally captures the flavor of the forecast for tonight, with the 1 inch confined to southern areas (I-94 south) and the 3 inches confined to far northern sections (M-46 north), with Tri-Cities region seeing additional snow early tomorrow morning to push totals to 4 inches or slightly greater. Tomorrow morning`s freezing rain impact will be dictated by exactly where the surface temps reside. Should be looking at the marginal 30-32 degree range vs more significant under 30 degrees for ice accumulation. It looks like the NAM has a bit of a cold bias (outside of the moderate snow areas) when comparing the temps over the Ohio Valley this evening. Once surface winds flip around to the south- southwest, right around 12z, will lose that dry near surface feed /wet-bulbing potential. The 12z European was one of the more aggressive solutions with the warm air moving in, leading to high confidence in a switch to light rain for most or all of southeast Michigan late in the morning/by Noon. Once again, inherited forecast and Winter Weather Message/Advisory looks in line and no significant deviations anticipated. && .PREV DISCUSSION... Issued at 630 PM EST Tue Dec 29 2020 AVIATION... Accumulating snow remains on target to develop late this evening/near midnight across southeast Michigan. Ceilings and visibilities should drop abruptly, with vsbys of 1/2-1SM and cigs aob 1000 feet. A dry slot will spread in overnight from south to north, ending snow overnight for most of the TAFS, MBS being the exception. Precipitation will then move back in 10-12z, and looks to be mostly in the form of freezing rain as warm and moist air surges into the state with increasing southerly winds, which look to gust aoa 20 knots during Wednesday. Higher dew pts in the mid to upper 30s should translate to IFR visibility and cigs and light rain for bulk of the day. Cold front/wind shift will occur late in the day (centered around or just after 20z), ending any precipitation. Still enough residual moisture with the brisk westerly winds to maintain high MVFR cigs through the evening. For DTW...Looking for up to an inch of snow accumulation centered around midnight, with snow ending between 2-3 AM. Freezing rain then expected to move in 6-7 AM, changing to rain 9-10 AM. DTW THRESHOLD PROBABILITIES... * Moderate for ceilings at or below 5000 feet around midnight tonight. High after 12z Wednesday. * High for precipitation type to start as all snow late tonight. * Moderate for freezing rain with some sleet 11-15z, then rain. PREV DISCUSSION... Issued at 419 PM EST Tue Dec 29 2020 DISCUSSION... Tranquil conditions across Southeast Michigan this afternoon with just a veil of transparent cirrostratus overhead. Strongly anticyclonic flow trajectories are in place between 925-575mb which is driving active subsidence within the layer. Antecedent dry air is forecasted to hold through approximately 02Z. The consistent trend in the model data has been towards a colder solution for the event tonight/Wednesday. Current observations are certainly eyebrow raising with surface dewpoints running in the teens. First part of the event will begin this evening as lead 800- 600mb warm advection wing lifts into Southeast Michigan. Plan view and cross section analysis depict sharp frontal structure on the 298- 305Ke surfaces that system relative isentropic ascent will be maximized on. X-section also show that a good connection exists between this midlevel frontal forcing with upper level jet forcing aloft. Very low static stability above the frontal surface with perhaps the models even suggesting some window for convectively unstable lapse rates at 600mb. Tally of QPF from the breadth of model solutions point to a brief 2 hour period of Moderate to Heavy snowfall rates from south to north between 02-08Z. There remains some concern that best frontal forcing and UVVS could bypass the far southern/eastern sections of the cwa. However, the HRRR and Rap remain very bullish tonight for Wayne/Monroe counties. 3 hour snowfall rates offered by the latest model data suggests upwards of 1 to 2 inches snow will be possible across northern Metro Detroit northward. Expectations are for a quick 1/2 to 1 inch southern metro Detroit. Cold temperatures in the middle to upper 20s overnight will maximize the accumulating potential. A lull in the precipitation is expected across the southern 2/3rds of the cwa overnight mainly between 06-10Z. For areas north of I 69 and M 46 forecast data shows main elevated frontal boundary lining out, parallel to the upwind flank of the +60 knot low level jet. Impressive signal for inflection point to 850-500mb 2d frontogenesis then persisting over the Tri Cities and northern Thumb region right through 15Z. NAM and RAP soundings are quite cold throughout the entire event, casting doubt on whether or not precipitation type will changeover to liquid. Given the look of the sounding, the feeling is could see more sleet than freezing with the cold air holding. Total snow accumulations of 2 to 4 inches will be possible in the Tri Cities and Thumb with locally higher amounts in northern Midland and Bay counties. The GFS is considered an outlier at this time. Farther south, the warm nose will be collocated with return of precipitation mainly after 10-11Z. A strong consensus exists that warm nose of greater than 3C will exist above 3000 ft agl with surface temperatures solidly holding below freezing through roughly 14Z. Virtually all model data is suggesting QPF amounts of up to 0.10 in freezing rain possible. Icy travel with snow covered roads, perhaps some icy untreated roadways. The decision was made to go with Winter Weather Advisory for all of Southeast Michigan from tonight through the Wednesday morning commute. Hazarouds travel conditions are expected during the Wednesday morning commute due to slippery roadways. The main trend for the New Year`s Day system is a slower onset of precipitation. Current storm track continues to favor a Gulf of Mexico low lifting into western Illinois 00Z Saturday the rocketing to far eastern Ontario and Quebec by 12Z Saturday. Latest information suggests a period of freezing rain will occur at the front end of the precipitation now well after 12Z. Very warm air is forecasted to lift through the region with 850mb temperatures potentially exceeding 8C right at the Lake Erie/Ohio stateline. MARINE... High pressure currently overhead departs tonight as the center moves from the Ohio Valley into the Northeast. The next low pressure system quickly follows lifting through the Upper Great Lakes Wednesday bringing with it rain and snow. Southerly flow increases Wednesday morning with gusts up to around 30kts across Lake Huron. There could be a brief couple hour period around 12Z where gusts could touch low-end gales, however, the duration is not expected to be long enough to require a warning. Winds rotate to southwesterly and eventually westerly over the course of the day with the cold front crossing the central Great Lakes Wednesday evening. This frontal passage will bring another uptick in wind strength with gusts reaching up to around 30kts, particularly over the northern half of Lake Huron. The pressure gradient over the region rapidly weakens Wednesday night as the low moves deeper into Canada and a new high begins to build over the Great Lakes. Light winds and dry weather are expected Thursday under this high before another large low lifts into the Great Lakes Friday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until noon EST Wednesday for MIZ047>049- 053>055-060>062. Winter Weather Advisory until 9 AM EST Wednesday for MIZ063-068>070- 075-076-082-083. Lake Huron...Small Craft Advisory from 4 AM to 4 PM EST Wednesday for LHZ442-443. Small Craft Advisory from 4 AM Wednesday to 4 AM EST Thursday for LHZ421-441. Lake St Clair...NONE. Michigan waters of Lake Erie...Small Craft Advisory from 4 AM to 4 PM EST Wednesday for LEZ444. && $$ UPDATE.......SF AVIATION.....SF DISCUSSION...CB MARINE.......KDK You can obtain your latest National Weather Service forecasts online at
Area Forecast Discussion
National Weather Service Grand Rapids MI
843 PM EST Tue Dec 29 2020 LATEST UPDATE... Update .SYNOPSIS... Issued at 228 PM EST Tue Dec 29 2020 - Impactful winter storm expected tonight into Wednesday morning - Wintry mix looking likely for Friday - Above normal temperatures over the weekend into early next week && .UPDATE... Issued at 842 PM EST Tue Dec 29 2020 At 0125Z KGRR radar trends and sfc obs indicate that the leading edge of the snow extends from around KMKG to KGRR. The snow will continue to advance to the northeast and quickly increase in intensity with snowfall rates up to around an inch per hour expected in the heaviest bands. Therefore hazardous travel conditions will continue to develop quickly across our area from sw to ne this evening. No significant fcst changes are needed. A consensus blend of latest high res short range guidance continues to show potential for around 4 to 7 inches of snow near to north/northwest of KGRR. We cannot rule out locally higher amounts to around 8 inches based on latest runs of the HRRR and overall guidance trends the past 12-24 hrs. Snowfall amounts south to southeast of KGRR will be considerably lighter where thermal profiles will moderate sufficiently enough overnight to cause pcpn to change to sleet and possibly a brief period of light freezing rain as well until sfc temps climb to above the freezing mark. So the mixed pcpn will limit potential for higher snow accumulations south/se of KGRR. && .DISCUSSION...(This evening through next Tuesday) Issued at 228 PM EST Tue Dec 29 2020 - Impactful winter storm expected tonight into Wednesday morning Looking upstream across Central IL into IA...the leading edge of the expanding area of snow has featured some heavier snow rates. Several sites are 1/4 mi or less. High res models do spread this snow into the CWA this evening. Trends have been for a little quicker arrival of the snow. Earlier today...we did bump up the start time of the winter weather advisory. It does look like southern zones could see an inch or two of snow quickly this evening before the main axis of precipitation shifts north towards Holland...Grand Rapids and Alma. At that point the band of steady to heavy snow stalls out. Thus...highest accumulations are projected to be along and north of a Holland to Grand Rapids to Alma line. This axis of heavier snow is a little further south than previous runs. A period of sleet or freezing rain will likely move into southern zones overnight...but qpf values are projected to be limited. Still...slick travel conditions are forecasted for the morning commute in all areas as temperatures are unlikely to go above freezing until after 8 or 9 am. The precipitation is expected to taper off from west to east late morning to early afternoon. - Wintry mix looking likely for Friday into Saturday The latest guidance continues to show a wintry mix of precipitation moving in Friday morning from the south. The precipitation then persists into Friday night...tapering off Saturday morning. The precipitation will not be steady...but it will occur in several rounds. This next storm appears to be more of a freezing rain/sleet event rather than a mostly snow event. Impacts look likely. Icy roads are expected to generate some of the impacts. As ice builds up on trees/power lines...some scattered power outages are possible. We will continue to message on the storm and provide social media guidance on it. - Above normal temperatures over the weekend into early next week Stronger warm air advection will occur across the Canadian Prairies over the weekend. This will act to shove the arctic air unusually far north for this time of the year. As a result...without any stronger cold fronts pushing down into MI...the region will see a period of above normal temperatures over the weekend and into next week. With some snow on the ground...temperatures should not stray too far above normal. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 527 PM EST Tue Dec 29 2020 Conditions will deteriorate rather rapidly to IFR during the mid to late evening hours tonight as snow moves in. Primarily IFR conditions will then continue at all the terminals overnight but there will be some variability during the early morning hours Wednesday as pcpn becomes mixed with and/or changes over to sleet and possibly light freezing rain. Steady mixed pcpn Wednesday morning will gradually taper off Wednesday afternoon but conditions will likely remain IFR to perhaps MVFR by late in the day. && .MARINE... Issued at 228 PM EST Tue Dec 29 2020 The onshore winds over 15 knots Wednesday into Wednesday night will support the hazardous conditions for small craft. The pressure gradient does weaken through Thursday so the winds and waves will likely decrease then. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until 1 PM EST Wednesday for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. LM...Small Craft Advisory until 10 AM EST Thursday for LMZ844>849. && $$ UPDATE...Laurens SYNOPSIS...MJS DISCUSSION...MJS AVIATION...Laurens MARINE...MJS
Area Forecast Discussion
National Weather Service Lincoln IL
837 PM CST Tue Dec 29 2020 .SYNOPSIS... Issued at 225 PM CST Tue Dec 29 2020 A storm system will move across the region through early Wednesday. A winter weather advisory in in effect northwest of the Illinois River for up to inch or two of snow and a tenth or two of ice as warmer air transitions the precipitation from snow to freezing rain this evening. Precipitation will go over to all rain after midnight as the warmer air filters into central Illinois. && .UPDATE... Issued at 828 PM CST Tue Dec 29 2020 Freezing rain is about to overspread areas northwest of the Illinois River Valley with icy accumulations expected over the next few hours. At this time, no major changes in thinking with up to a couple tenths of an inch of ice accumulations possible on untreated surfaces. Surface temps remain in the 28-32 range across this area with dew points in the lower to mid 20s giving a little room for temps to dip slightly due to evaporative cooling despite warm air advection occurring. RAP indicates the layer max 3C temp contour in the 925-700 layer has overspread the entire CWA so temperatures aloft are warm enough for full melting. Surface temps should rise above freezing between roughly midnight and 4 am. Further south, temperatures from IJX/SPI/AAA are 34/35/35, respectively, and mesonet sites across Schuyler and Menard counties show temps of 32-33 degrees. As such, the southern segment of the advisory should be able to expire on schedule at 9pm. This will include Schuyler, Mason, Cass, Scott, and Morgan counties. && .SHORT TERM...(This evening through Wednesday) ISSUED AT 225 PM CST Tue Dec 29 2020 Strong isentropic lift and 900-700 frontogenetic forcing from the NAM still suggests that best lift will occur late afternoon and early this evening over the far northwest portion of the forecast area with precip mainly in the form of snow. NBM and GEFS ensemble suggest while there is some potential for greater than a quarter inch of ice accumulation once warmer temperatures aloft advect into the area later this evening, However, overall thickness will likely remain lighter as the rain falls on snow cover already in place. Temperatures should rise above freezing by 07z throughout the region as the warm sector of the cyclone advects north of the forecast area. By sunrise, the cold front should begin to progress southeastward pushing the area of highest PoPs with it. By 00z Thursday, chance PoPs should be limited to near and south of I-70. Temperatures will are expected to fall behind the front and high temps will likely be during the morning. .LONG TERM...(Wednesday night through Tuesday) ISSUED AT 225 PM CST Tue Dec 29 2020 Broad southern stream trough centered along the California Coast is expected to dig into northeast Mexico over the next 24 hours before ejecting northward into the Midwest. Gulf of Mexico will be open and high water vapor transport values are expected to bring between a half inch and 1.5 inches of rain to the area Thursday Night and New Years Day. The warm sector surges northward as well and expect for the very start of precipitation, the phase should be mostly liquid with highs reaching the middle 30s in the GBG area to into the 50s near and southeast of I-70. Lots of uncertainty as to how fast the precip pulls out with deterministic GFS and ECMWF suggesting some snow/rain may stick around through Saturday, while several ensemble members push the precip south and east of the forecast area. For now will favor the drier scenario given the relative progressive flow. Arctic air cutoff from Illinois in the mostly zonal flow next week should keep temperatures mostly above normal at least into midweek. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 526 PM CST Tue Dec 29 2020 A warm front is lifting across central Illinois this evening with SE winds veering to southerly and strengthening aloft to 40-55kt resulting in LLWS. Meanwhile, spotty light precip will continue particularly at PIA where freezing rain is possible for several hours. Temps will eventually warm enough for all rain as precip coverage increases ahead of an approaching cold front. Moderate to heavy rain and IFR/LIFR conditions is expected overnight, then the cold front will mark the back edge of precip with winds turning NW and conditions improving slightly to MVFR. && .ILX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 4 AM CST Wednesday for ILZ027>031- 036-037. Winter Weather Advisory until 9 PM CST this evening for ILZ040- 041-047-049-050. && $$ UPDATE...Deubelbeiss SYNOPSIS...Barker SHORT TERM...Barker LONG TERM...Barker AVIATION...Deubelbeiss
Area Forecast Discussion
National Weather Service Jacksonville FL
808 PM EST Tue Dec 29 2020 .UPDATE... 00z soundings show a shallow moist layer around 5kft above the ground, beneath a big subsidence inversion. Radar has been recently showing a band of very light showers/sprinkles from coastal waters into Duval County...weakening as they spread further inland. Latest HRRR guidance suggests this pattern will continue through the night, with another very light band possibly developing over our southeastern GA coast. Keeping POP values low as likely most areas affected by band will only get Trace amounts. With surface dew points in the 40s to lower 50s...not expecting current temperatures to drop too much more, so not planning any significant changes to low temperature forecast in update. && .AVIATION... [Through 00Z Thursday] Satellite shows areas of CIGS BKN040-050 moving inland over eastern counties. Latest guidance suggests some lowering of CIGS down to BKN025-030 during the night...continuing during the day Wednesday, especially eastern TAF sites. && .MARINE... Winds will veer easterly tonight as high pressure elongates along the Atlantic Seaboard. An inverted trough of low pressure will develop in the easterly flow, leading to increase shower chances and cloud cover on Wednesday. Winds will shift southeasterly as high pressure builds into the Atlantic on Thursday ahead of the next frontal system. A cold front will approach from the west and eventually stall over the region late this week and into the weekend. RIP CURRENTS: NE FL & SE GA - Moderate Risk through Wednesday && .PRELIMINARY POINT TEMPS/POPS... AMG 47 66 54 76 62 / 10 20 20 30 20 SSI 53 66 57 71 62 / 20 20 20 20 10 JAX 53 71 58 77 64 / 20 20 10 10 10 SGJ 57 71 61 76 65 / 10 20 20 10 0 GNV 50 75 58 81 62 / 0 10 10 10 10 OCF 52 77 60 82 64 / 0 10 10 10 10 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...None. GA...None. AM...Small Craft Advisory from 4 AM Wednesday to 10 PM EST Friday for Waters from Altamaha Sound GA to Fernandina Beach FL from 20 to 60 NM-Waters from Fernandina Beach to St. Augustine FL from 20 to 60 NM-Waters from St. Augustine to Flagler Beach FL from 20 to 60 NM. &&
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
934 PM CST Tue Dec 29 2020 .UPDATE... 934 PM CST Our band of heavy snow earlier this evening is now transitioning over to a wintry mix. This trend will continue over the next few hours as strong warm air advection, via a 50-60kt low-level jet, continues to transport warmer air off the surface. This will support a period of sleet and freezing rain over the Chicago area for the next hour or so before the warm layer aloft becomes strong enough to support total melting of the hydrometeors, at which point we will see primarily freezing rain. More of a wintry mix is expected to continue up near the WI state line where the warm layer aloft could remain a bit weaker. It appears the Chicago area will have about a 3 to 5 hour window in which freezing precipitation will be favored before temperatures warm above freezing overnight. We are already seeing sites across central IL inch just above freezing, so it is just a matter of time before these warmer surface temperatures shift northward into the area. Unfortunately, until we climb above freezing we will see accumulating freezing rain, with a tenth or two possible before the change to rain occurs overnight. No changes are planned to headlines, but expect some improving conditions prior to the current ending times of these headlines. KJB && .SHORT TERM... 320 PM CST Through Wednesday night... As expected, top-down saturation process initially slow through mid day, has progressed rapidly within the last hour or so. Seeing moderate to heavy snow automated observations rather far south with this initial wave. Also received reports of snow almost immediately accumulating on roads upon onset of steady snow, backed up by area webcam observations. In what has been a month devoid of winter weather and associated impacts, this will be a higher impact event given the high snowfall rates into early this evening, followed by ice accumulations in the mid to late evening into the overnight as precipitation transitions over to brief sleet then freezing rain. The main change to the forecast to expand the Winter Storm Warning to include Kane, Lake (IL), and northern Cook (added as of just after 3pm) counties, per observational trends supporting another slight southward adjustment in the heavier snow axis, plus up to 1/10 to 2/10" ice accums tonight. Did not expand the Winter Weather Advisory to include any additional counties yet, but as mentioned in late morning AFD Update, may need to include Newton and Jasper Counties in Indiana for ice accumulation potential. However, confidence remains lower there, so will allow evening shift to closely monitor observational trends. /Technical Discussion/... The challenges with the forecast remain similar, namely the position of the heaviest snow axis into this evening, and then timing of expected transition over to sleet and then freezing rain in the mid-late evening into the overnight. As we`ve been advertising, the ingredients for moderate to heavy snowfall rates have most certainly materialized with the initial thump of warm advection snow rapidly onsetting this afternoon and continuing through the early to mid evening. Seeing numerous obs of 1/4 to 1/2 mile visibility and webcams and road reports with quickly snow covered roads. This is owing to radar indicating transient bands of embedded 30 to 35 dBZ echoes. The rapid onset of steady to heavy snow has quickly resulted in hazardous travel conditions down south of I-80. Snow band should be more transient in this area, so most of the snow for the event will be what has fallen and will fall over the next couple hours. Area of concern for perhaps overperforming snow totals and impacts would be northern half of LaSalle County, so will need to monitor for any headline changes there. As alluded to in previous update in the late morning, 12z OAX RAOB sampled steep (>7C/km) lapse rates above 550 mb within the DGZ, and did see some TSSN recently upstream over eastern Iowa. Seasonably high moisture (0.71" PWAT on SGF sounding) rapidly advecting northeastward is overlapping with the period of strong large scale (mid-level impulse and right entrance region of upper jet) and mesoscale (strong transient 850-700 mb f-gen) forcing through about 02z this evening. With what we`re already seeing, expect that the window of 1"/hr to even briefly 2"/hour snowfall rates will be about 2 to 4 hours, longest I-88 and north and shortest south of I-80. The high snowfall rates and periods of sharply reduced visibility are resulting in hazardous travel for the evening commute. Impressive alignment with the available moisture and strong forcing did also yield increased snow amounts in the heaviest axis across portions of far northern Illinois, with 5-9" messaged and localized 10" amounts possible closer to the WI state line in north central Illinois, depending on how long the heavy snowfall rates last. Earlier concern with respect to our headlines is the potential mentioned of the heaviest snow axis shifting a bit southward, and we did reflect this in the updated official forecast, along with the upgrade to warning for Kane, Lake (IL) and northern Cook County. The HRRR had consistently depicting this scenario (high liquid equivalent QPF as snow, brief intense hourly rates supported by forecast soundings). Confidence remains high that the 850 mb warm nose will be able to surge in this evening into the early overnight from southwest to northeast, and cause the p-type transition over to brief sleet and then freezing rain. While again the snow side is performing to earlier expectations or perhaps exceeding it, there`s signs on the observational trends back across southern Iowa and near-term guidance that the mix/change to brief sleet then freezing rain could occur a bit earlier this evening. This would be followed by steady rates, and potential for localized ice accums north of I-80 up to 0.2 to 0.25". This was also accounted for in our decision to upgrade some northern IL counties to a warning, and we`ll be watching closely for possibly needing any other short-fused changes. Otherwise, temperature trends will also be key tonight into early Wednesday, as longer duration of temps at or below freezing could spread ice accum risk a bit farther south, and necessitate expansion of WWA to Newton and Jasper Counties, though confidence is still low there. Temperature trends in northern Illinois will be key as to magnitude of travel impacts lingering into Wednesday morning, with some potential for locations in the far north staying close to 32F for longer. Most of the additional precip into the day on Wednesday will be out ahead of the approaching cold frontal trough and within areas that should be safely above freezing by then. The front will move through early in the northwest CWA and progress southeast from there, so highs only look to top out in the 33-36 range along and north/northwest of a Peru to Aurora to Highland Park line, with upper 30s southeast of that, and lower to mid 40s in the far southeast CWA. Expansive high pressure will move overhead Wednesday night, and low clouds will be scoured out. Should mid and high cloud cover be less than expected, forecast lows could end up colder over the remaining deeper snow covered areas of northern Illinois. For now, have close to seasonable lows, teens to lower 20s, in the official forecast. Castro && .LONG TERM... 224 PM CST Thursday through Tuesday... Confidence continues to increase that yet another winter weather event will impact our area centered on New Year`s Day as a low pressure system from the Gulf of Mexico lifts northward into the Great Lakes. Forecast thermal profiles continue to suggest initially light snow early Friday will transition to freezing rain after daybreak across much of the area, perhaps continuing well into the afternoon. A transition to "plain" liquid rain is also possible depending on the exact track of the low pressure system as well as how far north the freezing line manages to get (with a fresh snowpack from the system today and a dry/cooling northeasterly wind acting to keeping a good chunk of the area below freezing). Early numbers from the National Blend of Models (NBM) demonstrate that a glaze of ice is likely across the entire area with a fairly high signal (>70%) for a zone of more than a tenth of an inch somewhere across northern Illinois. Also, looking at this system with the CIPS Analogs (reanalysis based on the GFS forecast), 30-40 percent of the top 15 matches have at least three hours of freezing rain across northern Illinois. So, the key points for now are that we`ll have limited time to clean up after our system today/tonight and to prepare for another round of sloppy wintry weather late Thursday night into Friday. How quickly the system departs the region Friday Night-Saturday is an unknown (as it may slow). At any rate, long range guidance indicates a warming and dry conditions into the first full week of the new year. MTF/Borchardt && .AVIATION... For the 00Z TAFs... Aviation forecast concerns: * Period of moderate/heavy snow early this evening with LIFR conditions. * Snow transitions to a mix of snow/sleet/freezing rain mid to late evening, then to rain as surface temps warm above freezing pre-dawn. IFR ceilings prevail overnight into Wednesday morning. * Blustery southeast to winds gusting over 25 kt at times this evening, eventually shift southwest pre-dawn and west late Wednesday morning. * MVFR ceilings gradually improve through Wednesday evening. A band of moderate to heavy snow has lifted over the terminals as expected during the late afternoon hours, with snowfall rates of an inch per hour or more at times and visibilities at or below 1/2SM. Snow intensity/rates will begin to diminish by mid-evening, and may become mixed with sleet at times as warm air spreads in aloft. As this warming aloft continues, sleet/snow will transition to a period of freezing rain during the late evening with accretion rates of a few hundredths per hour. Surface temperatures will eventually climb slowly above freezing during the pre-dawn hours, roughly 08-10Z, with light rain then lingering through mid-morning Wednesday before ending. In total, snowfall across the Chicago terminals should range from about 1 to 4 inches (highest toward DPA and ORD), with ice amounts from a heavy glaze to around a tenth of an inch and possibly locally higher. For Rockford, moderate snow will persist through mid-evening with visibility in the 1/2 to 3/4SM range. Warming aloft should also produce a transition to a snow/sleet mix by mid-late evening and a mix of freezing rain/sleet and snow after midnight, before tapering to drizzle before ending during the pre-dawn hours. Total snow amounts of over 6 inches are likely at KRFD, with a glaze of ice. Surface winds across the terminals will be blustery from the southeast early this evening, then becoming south late. Gusts of 25 kts or more are possible. Winds become southwest after midnight, then turn westerly mid-morning Wednesday as the cold front moves through. Breezy west winds will then persist into Wednesday evening. Ratzer && .MARINE... 303 PM CST South to southeast winds will increase over the next few hours with gale force winds likely by late evening north of Chicago. Overnight, winds will gradually become southerly and then southwesterly by daybreak Wednesday with magnitudes decreasing in tandem. A Gale Warning remains in effect from Chicago northward through daybreak Wednesday. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Winter Storm Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010- ILZ011-ILZ012-ILZ103 until 9 AM Wednesday. Winter Weather Advisory...ILZ013-ILZ019-ILZ020-ILZ104-ILZ105- ILZ106 until 9 AM Wednesday. Winter Weather Advisory...ILZ021-ILZ023-ILZ032-ILZ107-ILZ108 until 6 AM Wednesday. IN...Winter Weather Advisory...INZ001-INZ002 until 6 AM Wednesday. LM...Gale Warning...Winthrop Harbor to Northerly Is. until 6 AM Wednesday. Small Craft Advisory...LMZ742 until 6 AM Wednesday. Small Craft Advisory...IN nearshore waters until 3 PM Wednesday. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
829 PM CST Tue Dec 29 2020 .UPDATE... Issued at 822 PM CST Tue Dec 29 2020 The forecast remains about on track for tonight. Temperatures have warmed to above freezing everywhere except Knox county where it was still hanging around 29 degrees at 830 PM. Will continue to monitor, but I don`t think it will be necessary to extend the Winter Weather Advisory. The RAP is showing the wind turning to the southeast over the next hour or two up there which should speed up the warming trend up in Knox county. The rest of the night just looks rainy ahead of the cold front as it moves slowly eastward. I don`t anticipate any big changes to the going forecast through Wednesday morning. Carney && .SHORT TERM... (Through Tonight...) Issued at 314 PM CST Tue Dec 29 2020 An area of precipitation continues across the northern CWA. Quincy is beginning to changeover to freezing rain or sleet from the snow that has been reported since late this morning. This trend will continue over northeast Missouri and west central Illinois into early this evening when warmer air over eastern Kansas and southern Missouri moves north and changes all precipitation into all rain. Will continue the advisory through mid-evening over the far northwest counties temperatures will rise above freezing in these counties early this evening. Mass fields from the short term models and latest runs of the CAMS still point to a lull in the precipitation for all but the far northwest part of the CWA later this afternoon and early this evening before a band of rain spreads back across the CWA from northwest to southeast tonight. This will occur as the upper trough currently over the Plains moves east tonight causing the attendant cold front also over the Plains to move into central and northeast Missouri by early tomorrow morning. Warm air advection ahead of the front will cause temperatures to rise the rest of the afternoon and then slowly rise or remain steady tonight. Britt .LONG TERM... (Wednesday through Next Tuesday) Issued at 314 PM CST Tue Dec 29 2020 Early Wednesday, the northern shortwave will be tracking across the upper Midwest with its associated surface low positioned across the Great Lakes. The surface low`s cold front will begin pushing across the CWA with widespread rainfall occurring along the front. As this front and associated precipitation continue pushing southeastward, cold air filtering in behind the front will allow for a transition to light snow on the back end of the precipitation during the evening and night. Only minor accumulations of around 0.1 are expected. As the front plunges into the Tennessee and Ohio vallies, it will stall, lingering the chance of precipitation across portions of southeastern Missouri and southwestern Illinois late Wednesday night and early Thursday morning. Here, temperature profiles during this portion of the period will support sleet and freezing rain, however, dry air advecting into the CWA behind the front may limit this threat. An additional factor that introduces a degree of uncertainty is the positioning of the front - more progressive movement will result in reduced precipitation chances. Current thinking is that sleet/ice accumulations of 0.1-0.2 inches are possible across portions of Reynolds, Iron, and Madison counties. During Thursday, our focus quickly turns to the next system. A shortwave digging southward across the western United States will kick a closed low located over northern Mexico into the Southern Plains. This closed low will continue to move nearly due north into the Middle Mississippi Valley, developing and bringing a surface low with it. The effects of this system will begin to be felt across southern portions of the CWA late Thursday afternoon and the entire CWA overnight as the precipitation shield advances northward. A warm layer seen in both deterministic and ensemble guidance will fully melt ice crystals that fall through the layer, and surface air will be at or just below freezing, bringing the threat of freezing rain through the CWA. However, there are several factors that will hinder ice accretion to some degree. First, the depth and temperature of the warm layer, which is forecast to be +5 to +10C, will couple with warming surface and ground temperatures. Second, high precipitation rates are expected, which is unfavorable for accretion. All that being said, it does look like there will be a window for ice accumulations of around 0.1-0.2 primarily across portions of central and northeastern Missouri and west-central Illinois where cooler surface temperatures will reside longer. As the surface low nudges into Missouri, precipitation will switch over to all rain across the CWA by Friday morning, and the axis of heavy snowfall will remain well to the west. Widespread rainfall is expected through mid-day Friday, with values of 1-1.5 inches possible in total. Runoff into waterways is greater this time of year, but river flooding continues to look unlikely. As the system exits the CWA later on Friday, it still appears possible that deformation zone may clip the northern portion of the CWA, bringing with it the chance for light snow. If this scenario occurs, light snow accumulations would be possible across portions of northeastern Missouri and west-central Illinois. Another chance for light snow is possible Friday night and Saturday as the aforementioned "kicker" shortwave moves through the Middle Mississippi Valley late Friday. Guidance has increased the amount of available moisture slightly, but confidence in precipitation is still low, so I have continued to keep this portion of the forecast dry. For Sunday through the end of the period, quiet weather is anticipated, and a warming trend will begin as temperatures increase to around 10 degrees above normal. Elmore && .AVIATION... (For the 00z TAFs through 00z Wednesday Evening) Issued at 543 PM CST Tue Dec 29 2020 MVFR ceilings are overspreading the area from the west and southwest. Expect lowering ceilings tonight as rain pushes from western and north central Missouri east across our area. Ceilings will eventually get down to IFR across the area by Wednesday morning as the front moves through. There will be a little bit more wintry precip across northeast Missouri and west central Illinois for the first few hours this evening, but temperatures are warming ahead of the cold front, so the threat for freezing rain should end by 02-04Z. Only rain is expected thereafter. Carney && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Winter Weather Advisory until 9 PM CST this evening for Knox MO- Lewis MO-Marion MO-Shelby MO. IL...Winter Weather Advisory until 9 PM CST this evening for Adams IL- Brown IL-Greene IL-Pike IL. && $$ WFO LSX
Area Forecast Discussion
National Weather Service Pocatello ID
204 PM MST Tue Dec 29 2020 .SHORT TERM...Through Thursday night. Fog and stratus remains a forecast concern tonight. This morning`s area of Fog has lifted into a well-defined stratus layer that is well entrenched within the entirety of the Treasure and Magic Valleys as well as the Snake Plain. Although the stratus layer has eroded a bit from the south, with slight warming above the stratus layer indicated on forecast soundings tonight, this will only serve to strengthen inversions and ensure that the stratus remains locked in. The HRRR and Nam3km performed admirably in their depictions of fog development and evolution last night, and these have been used to outline the fog areas once again tonight. Based on their depiction, fog should be somewhat less widespread tonight, and this makes sense given the dominance of the stratus layer. The best chance for dense freezing fog tonight looks to reside across the higher terrain of Lincoln and Minidoka counties north and east through the INL, Dubois and Island Park areas. Additional areas of freezing fog appear likely across valleys of the eastern highlands as well. Although the threat for fog along the Interstate corridors is lessened tonight with stratus preferred, we can`t rule out a few areas of fog here as well. Above the stratus layer, high level clouds will begin to gradually increase from the northwest after midnight in advance of our first in a series of incoming storm systems. Snow showers in association with the lead disturbance/warm advection regime will begin across the central Idaho mountains and Island Park region early Wednesday afternoon. Have increased snowfall totals and snowfall potential across the upper Snake Plain Wednesday afternoon, more in line with high-resolution guidance, as they indicate the seeder-feeder mechanism will be activated across this region. As a result, a quick 1-2" is possible from Idaho Falls north through Island Park, a few tenths more than the NBM depiction. Through the Wednesday evening hours, snow showers will gradually overspread the eastern highlands from north to south. No snow is expected Wednesday afternoon and evening across the eastern Magic Valley and extreme southern Snake Plain. Late Wednesday evening, a more robust round of snow showers will intensify across the central Idaho mountains, associated with the a second, stronger area of low pressure advancing southeast through Oregon. Snow associated with this wave will gradually expand south and east across the eastern Magic Valley, southern Snake Plain and south hills through the evening, continuing overnight. On Thursday, snow showers will be common across mainly high terrain areas of central and eastern Idaho, with northwest facing slopes favored. These snow showers will gradually come to an end Thursday evening and overnight, with dry conditions expected area-wide by daybreak Friday. 1-3 inches with as much as 5 inches over windward slopes is expected across higher terrain areas with this system, with generally 1" or less across the Snake Plain. An exception will be from Idaho Falls northward and in the Burley area, where 1-2" will be favored. Patchy freezing fog and stratus will once again be possible Friday morning on the heels of Thursday`s snow shower activity. AD .LONG TERM...Friday through Tuesday. Friday brings in a weak high pressure ridge building in between two areas of low pressure. Abundant moisture remains on track this weekend from an atmospheric river event. Snow showers will arrive in Central Idaho early Saturday with a chance for snow showers the remainder of the day in East Idaho. More boisterous snowfall remains on track for Sunday across our area; particularly in Central Idaho. Blowing snow is also likely to creep up as a weather impact across our area going through the day. Yet another shortwave trough will pass through the area Monday into Tuesday, bringing another period of snow showers. Yes, an Idaho winter pattern is upon us! ND && .AVIATION...Fog and low stratus challenges will persist in today and tonight`s forecast. The fog/low stratus will not completely go away but it is unlikely to impact all TAF sites throughout the entirety of the evening. Expect the bank to begin spreading back out overnight/early tomorrow morning once again. There is less certainty in the bank reaching BYI tomorrow and perhaps better chances for fog at DIJ. ND && .PIH WATCHES/WARNINGS/ADVISORIES... None. && $$