Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/19/21

Area Forecast Discussion
National Weather Service Binghamton NY
951 PM EST Thu Feb 18 2021 .SYNOPSIS... A disorganized series of upper level disturbances will move northeast from the Gulf of Mexico and up the eastern seaboard through Friday with light snow.Lake effect snow will start late Friday and continue into Saturday, and will be focused on areas north of the Finger Lakes and west of Syracuse with scattered snow showers elsewhere. && .NEAR TERM /THROUGH FRIDAY/... With the evening updates the main forecast update focused on adding patchy freezing drizzle to the forecast. Both the HRRR and NAM nest continue to indicate a lack of ice crystals in the clouds till precipitation ramps up overnight. 18Z model guidance along with the 00Z NAM and HRRR were also incorporated which did shift the main axis of accumulating snow slightly further east with each update lowering totals a touch as well. The forecast in Chemung county was revised downward enough to warrant the cancellation of the winter weather advisory given expected snowfall of only an inch or two. 225 PM update... Quick update for on-going trends. Main snow band stayed just south of the area, now we`re in a bit of a lull due to mid-level dry slotting between weak upper level disturbances. Frontogenesis band has been trying to get going straddling the NY/PA border and into the Catskills, but it has been battling the drier air aloft even as surface dewpoint depressions have narrowed. Outside of this band, some patchy freezing drizzle has also been reported, due to the lack of ice crystals in the dry slot. With the dry slot expected to diminish early this evening ahead of the next disturbance rippling up from the southwest, expect the risk of freezing drizzle to diminish a few hours from now. As mentioned yesterday, if the Wed Night/Thu AM snow failed to come through in the Southern Tier, we`d be hanging our hats on additional snow banding expected to develop tonight into Friday. Confidence is increasing for that scenario, even though the total snow amounts of 2 to 4 (locally 5) inches are a bit underwhelming for Advisory criteria. The impacts aren`t that much different one side of criteria or the other, and dropping the advisory before anticipated snowfall develops would be unwise. So, while the lack of snow today is far from ideal, we`ll let it ride. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... 355 PM update... By Friday evening, the synoptically-forced snow will have shifted east of the area and into the Hudson Valley and New England, with dry slotting in its wake quickly being replaced by scattered lake-effect snow bands and showers as northwest low level flow develops. The most persistent lake effect band will be focused along a trailing surface trough, which will enhance low-level convergence over eastern Lake Ontario, trailing into Onondaga County. This band may shift a little to the south and hug the southern shore of the lake heading into Saturday morning, with a fetch stretching back up to Lake Huron, further enhancing snowfall potential. Steep lapse rates from low level CAA and an approaching shortwave trough also favor the higher snowfall amounts. These factors should all help balance out the one limiting factor -- lake temperatures continue to cool. A Winter Storm Watch has been issued, focusing on northern Seneca, Cayuga, and western Onondaga Counties. If the CMCregional`s depiction pans out (and it`s not unlikely given the low level wind fetch), the band may end up extending well into Cortland and Chenango Counties for a time on Saturday afternoon. But, its residence time in those areas may be too short to really rack up the higher accumulations. Elsewhere, expect fairly widespread snow showers and snow squalls as a strong northern stream shortwave trough moves across the Niagara Peninsula Saturday morning, and into New England by Saturday evening. We`ll stay in cyclonic flow aloft through Saturday night, but negative vorticity advection in the wake of the shortwave trough should disrupt the lake effect bands to some degree Saturday evening. But, they may try to redevelop again before dawn Sunday, when low level winds should shift on the back side of an approaching ridge axis. Also, Saturday will be fairly blustery, with some gusts in the 20-25 mph range (even stronger gusts possible in snow squalls due to momentum transfer). Wind chill values will be in the teens. && .LONG TERM /SUNDAY THROUGH THURSDAY/... 355 PM Update... Lake effect snow showers will quickly diminish Sunday morning as high pressure approaches from the west. Otherwise, partly to mostly cloudy skies are expected with lows mainly in the lower to mid teens. Some single digit readings will be possible across northern Oneida County and the higher elevations of the Catskills. High pressure will briefly be in control on Sunday, which will bring partly to mostly sunny skies to the region. High temperatures will likely be in the upper 20s to lower 30s. Clouds then increase from west to east Sunday night ahead of the next system. A cold front will move through the area on Monday with one low pressure system tracking through the Great Lakes and another forming southeast of our region. This will bring light snow to the region, with rain likely mixing in for the valley locations as temperatures warm to above freezing. Highs are expected to be in the lower to upper 30s. Behind this front, some lake effect snow showers will be possible along the NY Thruway corridor Monday night. Then another weak system looks to bring snow showers, mixing with rain in the valley locations again on Tuesday. Highs Tuesday will likely be in the mid 30s to lower 40s. Lake effect snow showers then look to follow again for the NY Thruway corridor Tuesday night. High pressure will likely bring dry conditions on Wednesday before another system may bring a mix of rain and snow showers for Thursday. Temperatures look to be trending above normal with highs each day currently expected to be in the upper 30s to mid 40s. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Snow will increase during the overnight hours and continue into Friday. As snow moves across the terminals, expect visibilities to fall to between 1SM and 3SM with ceilings between 900 and 2000 feet. Some improvement in flight conditions is expected between 15z and 20z with IFR restrictions transitioning to MVFR. Winds will be easterly at 4 to 8 knots. Outlook... Friday night through Saturday night...Restrictions in CNY due to lake effect snow showers. Mainly VFR at AVP. Sunday through Sunday evening...Mainly VFR. Sunday overnight through Tuesday...A couple of systems will likely bring light snow and associated restrictions. && .BGM WATCHES/WARNINGS/ADVISORIES... PA...Winter Weather Advisory until 6 PM EST Friday for PAZ040-048- 072. Winter Weather Advisory until 1 PM EST Friday for PAZ038-039- 043-044-047. NY...Winter Weather Advisory until 6 PM EST Friday for NYZ057-062. Winter Weather Advisory until 1 PM EST Friday for NYZ055-056. Winter Storm Watch from Friday evening through Saturday evening for NYZ016>018. && $$ SYNOPSIS...MPH NEAR TERM...MPH/MWG SHORT TERM...MPH LONG TERM...BJG AVIATION...DJP
Area Forecast Discussion
National Weather Service Bismarck ND
920 PM CST Thu Feb 18 2021 .UPDATE... Issued at 911 PM CST Thu Feb 18 2021 Thus far fog has not developed across the northwest, but the latest iterations of the HRRR and RAP13 continue to show development in the next couple of hours. However, it is worth noting that observations still show rather large dewpoint depressions at the surface across many sites across the northwest and into Saskatchewan. Further east, into the north central a new patch of stratus has developed from central Renville county, south southeast through Minot, and into far northwestern Burleigh county. It looks as if this area of clouds should keep expanding while slowly drifting east. However, it is hard to say how long this batch of stratus will last and how widespread it may become as most guidance is handling the development poor. For this update, updated the sky forecast to better account for the latest observations and trends. Also tried to bump up low temperatures a bit where thicker cloud cover looks to be most likely. UPDATE Issued at 601 PM CST Thu Feb 18 2021 No major changes were needed for this update. The biggest challenge to the forecast tonight will be whether or not fog develops across the northwest. CAMs continue to have very different ideas about coverage and whether or not fog will even form. && .SHORT TERM...(This evening through Friday) Issued at 253 PM CST Thu Feb 18 2021 A possibility of fog in the west and relatively warmer temperatures tomorrow highlight the short term forecast. Tonight behind the exiting trough, anticyclonic flow will take over with a building shortwave ridge in the west. Stratus and scattered flurries may linger in the east under the periphery of the exiting cyclonic rotation, with mostly clear skies in the west. With the diffuse pressure pattern and the current snowpack, fog may develop in areas of the west tonight and early Friday morning. High-res guidance is inconsistent in placement, with the 18Z RAP being the most enthusiastic about fog potential in the northwest. Fog was kept out of the forecast for now but trends will need monitoring. Warmer temperatures expected Friday with low level warm air advection gradually taking place. Highs in the 30s southwest and teens east expected. .LONG TERM...(Friday night through Thursday) Issued at 253 PM CST Thu Feb 18 2021 A chance of light snow Friday night followed by warmer temperatures and a possibly windy Monday highlight the long term forecast. Upper level flow becomes quasi-zonal through the weekend with gradually warming temperatures at the surface. A weak wave should push through the flow Friday night through Saturday morning which should bring a chance of light snow across much of the west and central. Otherwise the story remains consistent with highs forecast to reach the 30s and low 40s by Sunday. On Monday a mild Pacific air mass arrives along with the nose of an upper level jet. Warm and possibly windy conditions are should accompany this arrival, before the jet dives south by mid-week. NBM/MEX/ECM guidance consistently advertises highs on Monday to reach around 50 in the southwest and 40s elsewhere, which looks reasonable. 12Z guidance along with NBM probabilities are in good agreement in a relative cool down mid-week with highs in the 20s and 30s. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 601 PM CST Thu Feb 18 2021 Stratus has nearly eroded across the forecast area and VFR conditions area expected to prevail through he period. The one exception could be if fog forms across the northwest tonight which would mainly impact KXWA. Considerable uncertainty remains about whether fog will even form so have not included it in the TAF forecast at this time but the potential is there. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...ZH SHORT TERM...AE LONG TERM...AE AVIATION...ZH
Area Forecast Discussion
National Weather Service State College PA
1037 PM EST Thu Feb 18 2021 .SYNOPSIS... Light snow and some mixed precipitation Friday morning before ending in most places by Friday afternoon. Snow showers will linger over the western Alleghenies into the weekend, while other locations see drying/improving conditions into Sunday. A fast moving system will likely bring a period of rain and snow from late Sunday night through Monday. Beyond the early-week system, the weather pattern through the end of February looks less stormy with warmer temperatures trending near to above average. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Modest warm advection ahead of approaching shortwave and weak surface low over Ohio will result in occasional light snow across much of central Pa overnight. Some freezing drizzle has been noted across the Lower Susq Valley this evening. However, IR loop and RAP soundings indicate the arrival of deeper moisture and associated colder cloud tops will result in any fzdz changing back to light snow down there by around 03Z. Latest NBM qpf supports additional accumulations between 00Z-12Z of an inch or less. Temperatures should remain steady in the 20s overnight under cloud cover and weak warm advection. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Light warm advection snow should taper off from west to east Friday morning, as mid level shortwave and associated occluded front push through. Behind this feature, focus will shift to light, lake enhanced, orographic snow showers across the Alleghenies, as a seasonably cold air mass crosses the Grt Lks. Model soundings indicate cloud top temperatures are likely to be just above -10C during late morning and early afternoon over the Alleghenies, so will mention the possibility of spotty freezing drizzle in that area. Surface ridging and associated low inversion heights will result in only minor snow accums of less than an inch over the Alleghenies Friday and Friday night. Elsewhere, downsloping west-northwest flow behind occluded front should result in breaking clouds east of the Appalachians by Friday afternoon. Model RH profiles suggest skies will become mostly clear across the Susq Valley Friday night. Low level chill should be scoured out with arrival of occluded front Friday, resulting in temperatures rising into the mid and upper 30s by afternoon over the eastern half of the forecast area. A return to below normal temperatures is expected Friday night, as cold advection kicks in. NBM mins range from the teens over the Allegheny Plateau, to the low 20s over the Lower Susq Valley. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... 12 noon update... In the big picture, the upper-level pattern is expected to relax across much of the CONUS through next week. This takes place as the deep central Canadian vortex retreats and heights rise for most areas. Specifically for the Commonwealth, this should lead to a less stormy pattern, with moderating temperatures. As for the daily sensible weather, we`ll still have lingering cold and moisture into Saturday behind the storm system currently affecting the region. This scenario should produce some residual lake enhanced and upslope snow showers/flurries over the northern tier and along the Allegheny Front. Dry weather is expected Sunday as a weak high pressure ridge builds across the area. A fast moving wave of low pressure and associated frontal complex are expected to cross the Commonwealth late Sunday night and Monday, associated with the likelihood of light snow north of I-80 and a rain/snow mix farther south. Any light lake enhanced and upslope rain/snow showers behind this system look inconsequential from this early vantage point, as the incoming air mass for the middle of next week doesn`t appear to be particularly cold. && .AVIATION /04Z FRIDAY THROUGH TUESDAY/... Restrictions will be widespread overnight owing to ongoing snow in the central and western areas with freezing drizzle at MDT and LNS. As of 00Z, a band of snow showers extends from JST/AOO to IPT via UNV. This band of showers is expected to persist for the next several hours. Additionally, current radar trends indicate a developing band of snow that will affect BFD through 02 or 03Z. Ceiling restrictions will persist through daybreak tomorrow, though snow will lift out from SW to NE after midnight with visibility improvements following soon after. As winds turn to come out of the NW during the day Friday, downsloping will help to improve ceilings and eventually clear skies out in the central and southeastern airfields. Outlook... Fri...Lingering snow showers north and east through midday. Improving conditions elsewhere. Sat...Mainly dry w/ VFR conditions. Sun...Prevailing VFR. Increasing clouds. Chance of snow west late. Mon...Widespread reductions in rain/snow. Tues...Lake effect snow showers to bring reduced cigs/vis to BFD & possibly IPT/JST && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 10 AM EST Friday for PAZ035-036- 056>059-063>066. && $$ SYNOPSIS...DeVoir NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald LONG TERM...Jurewicz/Gartner AVIATION...Banghoff
Area Forecast Discussion
National Weather Service Grand Rapids MI
700 PM EST Thu Feb 18 2021 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 320 PM EST Thu Feb 18 2021 - Lake enhanced snow showers Friday with some accumulation - System snow Sunday night into early Monday - Another weak front early Tuesday - Warmer most of next week with possible system Thursday && .DISCUSSION...(This evening through next Thursday) Issued at 320 PM EST Thu Feb 18 2021 - Lake enhanced snow showers Friday with some accumulation - The light snow from the system passing south of us this evening should end by evening as the deep moisture pulls out. I do not see any significant accumulation from the snow this afternoon into this evening. The snow event on Friday during the day will very likely bring some locally heavy snow showers to our area. There are now two parts to this event. The first part is the low level winds being pushed from easterly to westerly around sunrise Friday. The second part as a shortwave associated with the coldest air, that moves through Friday evening. Warm advection at mid levels starts after midnight so that will slowly end the snow showers during Saturday morning. Meanwhile the DGZ is below 6000 ft Friday but there is strong lift in it for both events (mid morning and late afternoon into the evening). We will still be in the deep cold air during this entire event too so it should be no problem to generate lake enhanced snow showers. The HRRR has 12 hour localized precipitation amounts over 0.7 inches near MKG by evening, given a 20:1 ratio that would be over a foot of snow if it happened. Also, it is worth noting that most of that falls with the second shortwave during the evening. Also remember the higher amounts will be very localized. This may be a slow evening commute along US-31 from Ludington to Grand Haven. Even so, most areas would get less than 2 inches Friday. Also, due to the wind being mostly westerly the snow showers will get all the way across the CWA during the day on Friday. Cloud level winds will be mostly less than 20 knots, normally that would not bring the snow bands too far inland. However this synoptically forced as it is really a weak cold front crossing the area. The evening event will mostly stay near and west of US-131. This is when the heavier snow showers are expected. We could see localized snowfall rates over over 1 inch per hour in the better snow bands. - System snow Sunday night into early Monday - The next system is the last (so we think) significant snow producing system in the colder weather pattern we have been in. It is this system that boots the cold air out of here. The Sunday system was the trailing shortwave that dug into west side of the central CONUS upper trough. We are in the jet exit region on this system. That should help us stay cold enough for all snow. The 1000/850 moisture transport vectors are aimed at I-94 Sunday evening with a flow coming from the Gulf. This will likely be a 6 hour snow event with a 3 hour period of moderate to heavy snow. This system will bring a quick 2 to 4 inches across the area. Maybe areas north of I-96 could see 3 to 5 inches due to the moisture transport being so well aimed at us while we are in the jet exit region. Seems the surface low will largely stay near or south our CWA so it will be all snow. It should be too warm for lake effect snow behind this system though. Once this system moves out of this area, we will have a more zonal flow through next week. - Another weak front early Tuesday - The lead shortwave moves on large polar jet core from the Pacific, across the area early Tuesday. That may result in some light snow showers but nothing of consequence. By then it will be just cold enough for snow but no cold enough to create lake effect. I will admit this may end but being more than just flurries since we have the exit region of a 150 knot jet causing it. This will be another feature to watch out for. - Warmer most of next week with possible system Thursday - That 150 knot jet exit region is from a broad upper jet that extends across 40 degrees of longitude. The system behind that digs a trough on the west coast, which in turn lifts that jet north of us by Wednesday. We will then be on the anticyclonic side of the polar jet and should be in the warm air. Well at least sort of anyway. Here is where it gets glitchy. That large jet streak moves east and we are in the entrance region of that jet by early Thursday. Then there is a southern stream jet feature coming out of the base of the trough, created by that next Pacific system. The latest ECMWF couples the two jets (exit region incoming southern stream jet with the entrance region of the departing northern stream jet). That of creates enough lift for a broad area of precipitation from central New York State, across lower Michigan, into Iowa early Thursday. This could be mixed precipitation here or maybe just snow we will have to see. The GFS does is similar with the upper air pattern has but no precipitation with the event. Again this is yet another event to watch. So there is the bottom line, while it may seem we could have a dry period of weather next week, it just may turn out not nearly as dry as we were thinking. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 700 PM EST Thu Feb 18 2021 Light snow will continue to produce widespread MVFR vsbys between 3 and 5 miles this evening, primarily south and east of GRR. Some brief/localized IFR vsbys are also possible. As that snow pulls away later tonight, we may see several hours of VFR in it`s wake. However as lake effect snow develops Friday, expect MVFR or lower cigs/vsbys to redevelop. That will occur first at the lakeshore (MKG) around 12Z, reaching inland toward LAN/JXN by afternoon. Some of the snow showers Friday could be locally heavy at times so brief LIFR vsbys are possible. && .MARINE... Issued at 320 PM EST Thu Feb 18 2021 At this point we do not have enough wind with any of the system moving through the area into early next week to be very concerned about issuing marine headlines. The ice build up in the near shore helps to mitigate some of that anyway. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ SYNOPSIS...WDM DISCUSSION...WDM AVIATION...Meade MARINE...WDM
Area Forecast Discussion
National Weather Service New Orleans LA
836 PM CST Thu Feb 18 2021 .UPDATE...Forecast is running on track for the most part. A few sites are running a little slower this evening but the forecast lows still look good for a majority of the area, maybe a few southshore sites forecast could be a tad to warm but will hold off on an adjustments at this time. Looking downstream slightly drier air has started to work southeast once again and dewpoints are still forecast to drop into the mid 20s to lower/mid 30s across the area however, the concern for tonight could be winds. Winds are forecast to not decouple and could remain around 15-20kts at h925. Other concern is how strong is the CAA? Looking at the latest HRRR it initialized too cool in the LL. Our 00z sndg at h925/h85 was 7C and 9.5C respectively (HRRR was 4C and 9C) while JAN`s 00z sndg measured -1C and 4C (HRRR -2C and 1C). Too offset the wind expected tonight CAA needs to be strong and not really seeing a lot to indicate overpowering CAA. That said there is drier and colder air sliding in and if for some reason winds shut down and hour or two before sunrise temps could drop pretty good in a short time and we would hate to make any significant changes to the forecast or cancel any warnings at this time but it wouldn`t be a shock if we just don`t reach our potential tonight. Tomorrow night is a different story and could be a VERY good radiational cooling set up. /CAB/ && .PREV DISCUSSION... /issued 336 PM CST Thu Feb 18 2021/ SHORT TERM (Tonight through Saturday Night)...A longwave trough axis will sweep through the Gulf South tonight into tomorrow. The main impact from this trough axis will be a pool of much colder air advecting into the region, and the continuation of cloud cover through tomorrow morning. Temperatures will fall below freezing across the entire forecast area tonight, and a hard freeze with readings 23 to 26 degrees is expected for areas along and north of I-12. The thermal trough will remain over the area tomorrow, and daytime highs will struggle to reach the middle to upper 40s even with ample solar insolation in the afternoon hours. The coldest night of the period will occur tomorrow night due to a combination of light winds and clear skies. Lows will once again fall below hard freeze criteria for areas along and north of the I-12 corridor with readings in the upper 20s and lower 30s across the remainder of the area. Another round of freeze and hard freeze warnings can be expected. Have opted to go slightly colder than guidance through tomorrow night given the extensive snowpack just north of the CWA. Saturday will be a day of transition as the trough axis pulls to the east and a weak upper level ridge moves in from the west. Increasing subsidence aloft will clear skies and warmer temperatures to the area. Highs will remain about 10 to 15 degrees cooler than normal, but will warm into the middle to upper 50s. This same trend will continue into Saturday night as temperatures fall into the lower to middle 30s north of I-10/12 and the lower 40s south of the tidal lakes and along the Louisiana coast. LONG TERM (Sunday through Thursday)...The weak ridge axis will shift to the east on Sunday, and an increase in cloud cover is expected through the day as a shallow shortwave trough and associated front moves into the Southern Plains. The combination of increasing lift in advance of this trough and some moderate return flow around 850mb will be sufficient enough to bring increasing cloud cover to the area throughout the day. Warmer temperatures can also be expected with this return flow off the Gulf, and highs should be closer to average in the mid 60s. The weak shortwave trough will push through the Gulf South Sunday into Monday, and surface front will accompany this trough axis. Increased low level forcing along the frontal boundary will combine with stronger lift aloft to spark off scattered showers Sunday night into Monday morning. The POP forecast will still be relatively low at 20 to 40 percent during this period, and instability parameters will remain very weak. As a result, thunderstorm activity is not anticipated with this frontal passage Sunday night. Temperatures will be near average Sunday night with lows in the 40s and lower 50s, but some weak cold air advection into the area on Monday will cool temperatures a few degrees into the upper 50s and lower 60s. The main heart of the cold pool will pass over the area Monday night and lows should dip into the upper 30s and lower 40s. A return to weak upper level ridging and increased subsidence aloft along with southerly flow in the low levels will lead to clearing skies and warmer temperatures for the middle of next week. Highs should climb back to more normal readings in the upper 60s and lower 70s by Wednesday and overnight lows will warm from the 40s Tuesday night into the 50s by Wednesday night. Cloud cover should also increase Wednesday night due to a combination of the warmer air advecting in from the south over the cooler nearshore waters, and the approach of another low pressure system. This system should impact the area at some point late next week, but timing differences between model solutions are in place. Have opted to stick with a blended solution and indicate low end chance POP for Thursday. Temperatures will remain near average with highs in the upper 60s and lower 70s expected. && .AVIATION (00Z TAF DISCUSSION)...Low stratus will linger over the terminals until around 15z in the morning. IFR ceilings are expected at all of the terminals during this period. Winds will also remain gusty from the north at more than 12 knots at KNEW and KMSY as boundary layer winds mix down to the surface after passing over the warmer lake waters. After 15z, skies are expected to clear rapidly as drier air aloft mixes down, and prevailing VFR conditions can be expected through the end of the forecast period. && .MARINE...Strong gradient flow associated with a colder airmass moving into the area will keep winds and seas elevated into small craft advisory range through tomorrow evening over the open Gulf waters. In the lakes, the winds should begin to decrease below advisory levels later tonight. The surface high associated with this colder airmass will shift toward the eastern Gulf over the weekend, a onshore flow of around 15 knots is expected to take hold of the coastal waters. This onshore flow will continue through Sunday night before another cold front moves through. Winds will shift back to the north at around 15 knots by Monday and remain from the north through the first half of next week. && .PRELIMINARY POINT TEMPS/POPS... MCB 24 44 20 57 / 0 0 0 0 BTR 26 45 23 55 / 0 0 0 0 ASD 28 49 24 59 / 0 0 0 0 MSY 32 48 31 56 / 0 0 0 0 GPT 31 50 27 57 / 0 0 0 0 PQL 31 50 25 58 / 0 0 0 0 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...Freeze Warning from midnight tonight to 9 AM CST Friday for LAZ056>070. Hard Freeze Warning until 9 AM CST Friday for LAZ034>037-039-040- 046>050-071-072. GM...Small Craft Advisory until midnight CST Friday night for GMZ532- 536-538-550-552-555-557-570-572-575-577. Small Craft Advisory until 3 AM CST Friday for GMZ530-534. MS...Hard Freeze Warning until 9 AM CST Friday for MSZ068>071-077. GM...Small Craft Advisory until midnight CST Friday night for GMZ536- 538-550-552-555-557-570-572-575-577. Small Craft Advisory until 3 AM CST Friday for GMZ534. && $$
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
857 PM CST Thu Feb 18 2021 .UPDATE... 857 PM CST Forecast in generally good shape this evening. Other than keeping a mention of flurries beyond midnight for northern/northeast IL and adjusting some hourly temp trends for effects of variable cloud cover, see little that needs significant changes. Radar trends this evening have indicated a gradual reduction in snow shower intensity in inland areas with the loss of diurnally enhanced low level instability after sunset. Backing of the low level wind field from northeast to north-northwest over southern Lake Michigan has also allowed for a decrease in lake-effect snow showers, though less organized lake-induced light snow does persist from along the Cook county shore into northwest Indiana. This should continue to shift southeastward out of Chicago over the next couple of hours as winds continue to back more west- northwesterly, with light snow showers persisting and gradually shifting east across northwest IN overnight. Across north central and northeast IL, continue to see a bloom of weak radar returns (in sensitive VCP-31 mode) associated with flurries. This appears to be in association with forcing tied to the approach of a compact mid-level short wave over eastern IA, which will translate eastward across northern IL through 06-09Z. 00Z DVN sounding and RAP initialized forecast soundings suggest moisture is fairly shallow, but right in the -10C to -20C range perfect for squeezing out a few flakes with the assist from the approaching wave. The short wave trough/vort axis looks to move through the Chicago area by 3-4 am, which should allow any lingering flurries to end. Otherwise, GOES IR depicts areas of stratus/stratocu which will bring partly to mostly cloudy skies across a good portion of the area into the pre-dawn hours. However, where clearing or breaks in the cloud cover occur, sharp temp drops are likely (KARR dropped to 10 as clouds scattered out, but has risen back to 16 as clouds moved back in). Wouldn`t be surprised to see a few spots dip below zero by morning, but for now think going forecast has a decent handle on things with lows approaching zero across a good portion of northern IL and higher single digits into the heart of the metro and northwest IN. Ratzer && .SHORT TERM... 205 PM CST Through Friday night... Our earlier cohesive area of steady lake-enhanced snow has become notably more cellular in nature. With surface temperatures having risen into the low to mid 20s, steepened low-level lapse rates have allowed a sliver of surface-based instability to develop. Where this has co-located with enhanced near-surface convergence, we`re seeing a decent coverage of snow showers rotating south and westward across parts of northeast Illinois. Anticipate that these will begin to wane with the loss of heating through the rest of the afternoon and into the evening hours, but have maintained a pocket of likely PoPs to account for this the rest of the afternoon. Locally sharply varying visibilities to under 1-2 miles are likely with this activity, although what seems to be fairly large flake sizes will help hold the visibilities up a bit more than we`d otherwise expect given the radar reflectivities. Am somewhat uncertain how additional lake effect may evolve this evening and overnight. With the low-level flow becoming more west to northwesterly with time, the expectation is for any lingering LES to begin to slosh eastward more into NW Indiana. This idea seems to be supported reasonably well with this afternoon`s guidance and have limited things to just a mention of flurries later this evening across parts of northeast Illinois as a result, transitioning to somewhat better snow chances into Lake and Porter counties. Increasing low-level winds with time should hold the residence time of any lake band down, but given high ratios, couldn`t rule out a quick inch or so towards and just after midnight tonight. Our next disturbance, currently pinwheeling across the Dakotas, is forecast to push into our region later on Friday afternoon and evening. While the ECMWF and EPS remains precipitation-free, the GFS/GEFS, and CMC/GEPS continue to squeeze out some light precipitation amounts south of I-80 where enhanced low-level moisture coincides with better near-surface lapse rates. Given how sharp this feature appears on upstream moisture channel loops, did elect to throw in some low-grade snow chances into Friday evening, although note that this remains a somewhat lower confidence forecast. Depending on how fast this system scoots east of the region, slackening winds and potentially clearing skies as a surface ridge builds overhead could allow patchy (freezing) fog development, but this remains too conditional to warrant a mention in the gridded forecast at this time. Carlaw && .LONG TERM... 248 PM CST Saturday through Thursday... Generally quiet conditions are expected for the start of the weekend as the persistent upper-low and broader loosely blocked pattern continues to break down. Weak low-level WAA will lift northeast across the CWA midday into the evening under a passing mid-level speed max. Have kept the forecast dry for now, but if there is any semblance of thicker stratus over the area, a light wintry mix of fine snow and freezing drizzle cannot be ruled out. Focus then turns to the potential for accumulating snow area-wide Sunday and Sunday night. A slow-moving mid-level trough over the central Rockies Saturday night will slightly phase with another trough tracking ESE though south-central Canada. While the resulting low-level surface and 850 hPa lows will not have the typical favorable track for heavy snow across northern Illinois, tracking from southern Iowa into southeast Wisconsin in this case, the combination of a slightly negative tilt to the mid-level trough and corresponding steep lapse rates aloft indicate that this system has the potential to produce a period of moderate to briefly heavy snow. Thermo profiles showing limited DGZ depth amid continued low-level WAA favor SLR values in the 10-13:1 range. While there may be enough WAA to allow for some rain to mix with the snow across the far southeast CWA, wetbulb profiles and dynamic cooling favor all snow as the precip type for much of the area. Timing from ensemble and deterministic guidance continues to become more refined, with snow spreading west to east across the area late Sunday morning west of I-39 to early/mid afternoon in the Chicago metro and northwest Indiana. Steady light to moderate snow with some pockets of briefly heavy snow will likely continue through the evening before tapering from west to east overnight. While confidence in accumulating snow is quite high, confidence in amounts is much lower. Timing will be critical in order to see higher amounts as low-level moisture transport ahead of the system will be commencing right as it is progged to move across the CWA. Conservative estimates yield 1.5-3" for much of the area, with a higher-end potential of a narrow swath of 3-5". Given the decent dynamics and lapse rates in play, high snowfall rates will be possible with most of the snow falling in 9 hours or less. Beyond Sunday, the cold pattern that has been locked in place across the area will finally break, giving way to more seasonable temperatures well into the 30s for much of the upcoming week. Even with the warmer conditions, the amount of snow melt is less clear with nighttime temps falling back below freezing, the necessity to warm/prime the existing snowpack, and some potentially breezy periods amid drier conditions. And while sunny days will help melt snow at the top of the snowpack, the snowpack is likely deep enough to absorb and hold onto much of this melt water. With all that said, any substantial days of melting will increase flooding concerns. Kluber && .AVIATION... For the 18Z TAFs... A somewhat lower confidence forecast through the next 6-9 hours or so with persistent lake-enhanced snowfall pivoting across northern Illinois. Prevailing MVFR/IFR -SN appears to be gradually pushing inland at this time, with light east to northeasterly winds noted now near the lake. Based on the TORD TDWR, it looks like there may be one last push of IFR -SN to push across the ORD/MDW airfield through 20z or so with perhaps an additional one half inch of fluffy accumulation. Based on visible satellite imagery and some recently shared photos from the Chicago area, bonafide cumulus is developing with a bit of daytime heating. Guidance suggesting a semi-broken line of snow showers seems plausible as a result along the enhanced area of surface convergence. Given a hint of instability at the surface, any snow showers could lay down some decent rates (for brief periods), and have introduced a TEMPO for 2 sm -SN at DPA as a result. At this time, the thinking is this SHSN type activity will develop west of the ORD/MDW terminals but may impact DPA into the mid-afternoon hours. RFD looks to be far enough west to maintain just occasional flurries into this evening. GYY offers up a conundrum, as it`s conceivable additional lake effect snow develops and pushes south off the lake this evening. This signal isn`t terribly strong at this time, but sufficient to justify a PROB30 for -SN overnight. Otherwise, activity should diminish this evening with winds trending northwest and eventually westerly. Could develop some occasional gustiness Friday afternoon as well. Another wave will pass overhead, and it`s possible this also squeezes out some additional snow showers. Latest indications are this activity may not develop until closer to Friday evening. Carlaw && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
National Weather Service Morristown TN
1008 PM EST Thu Feb 18 2021 .UPDATE... EVENING UPDATE. && .DISCUSSION... The forecast remains on track for the overnight. Just inputed recent observations of temps, dew points, and winds to adjust the hourly curve. Latest RAP analysis places the cold front just E of the S Appalachians, but the colder air has been slow to cross the Cumberland Plateau into our region. Current temps W of the Plateau are in the upper 20`s, with mostly upper 30`s/low 40`s in our region. This cold air W of the Plateau will spill in over the next few hours. Lift from a 160 kt jet overhead has worked with abundant low-level moisture to continue areas of light rain and drizzle through the evening, and this will continue through about 06Z before changing to light snow showers and flurries from W to E as the colder air finally works into the region. At the same time however, forecast soundings show the low-level moisture beginning to erode after 06Z, so expect any light accumulations to be confined to the higher terrain of the Plateau and E TN/SW VA mountains late tonight. Slightly higher amounts of up to 1 inch are still expected in the E TN mountains as weak NW upslope flow kicks in. Garuckas && .AVIATION... 00Z TAF DISCUSSION. Poor flight conditions with drizzle, mist, and IFR will continue through the evening at CHA and for most of the night at TYS and TRI. Used TEMPO groups for brief LIFR at TYS and TRI this evening. Drier air building in will allow CHA to scatter out to VFR by mid morning Friday, but it will take until late afternoon for TYS and TRI to return to VFR. Winds will generally be N to NW at 3 to 8 kts through the period, except NE at times at TYS. Garuckas && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 29 43 22 47 27 / 20 0 0 0 0 Knoxville McGhee Tyson Airport, TN 29 39 20 42 25 / 30 10 0 0 0 Oak Ridge, TN 28 40 18 42 25 / 30 0 0 0 0 Tri Cities Airport, TN 31 38 18 38 23 / 40 10 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$
...Updated Aviation Forecast Discussion...

.DISCUSSION... Issued at 250 PM CST Thu Feb 18 2021 The primary forecast concerns are chances for light snow or light freezing drizzle Saturday night into Sunday. We could also see a little light snow tonight. Large scale mid tropospheric pattern features a trough extending from MN down into west TX, with a ridge from British Columbia to off the coast of CA. There does appear to be a weak shortwave trough moving southeast across the central US now. 2 pm surface analysis showed high pressure dominating much of the region. Tonight, it does appear that there will be some potential for light snow or snow flurries as an area of moisture and lift move through the area. Cloud temperatures have been favorable for ice crystal growth the past 24 hours or so and that appears that it will continue tonight. Recent RAP model runs continue to depict potential for an area of light snow moving from west to east through the area overnight, in association with a another trough in the northwest flow. Right now it appears amounts of an tenth of an inch or two are possible. Temperatures have warmed up into the upper teens and lower 20s at most spots with dewpoints in the single digits and teens. Lows tonight are tricky with the variable cloud cover, snow cover and fairly light winds. Expect most lows in the single digits, but localized radiational cooling could result in some lows below zero. We will see a gradual warming trend the next few days. Areas near the SD and KS borders could approach freezing tomorrow, with many spots in the 30s Saturday. The next disturbance of concern will start to approach from the west Saturday night. Large scale lift will increase, but there is some question as to moisture depth and amount of ice aloft. Some soundings show the moisture too shallow to generate ice and dry layers aloft. For now we will keep a mention of both light snow and freezing drizzle, with details likely becoming more clear the next few model runs. There appears to be potential for around 1 inch of snow and a light glaze of ice with this system. Chances will mostly be in the decrease Sunday afternoon and we look for highs in the lower or mid 30s. The big story next week is warmer temperatures. We should see highs in the 40s Monday, with 40s to lower 50s Tuesday. The warmest highs should be where snow cover is the lowest. It looks like a cooler airmass will move in Tuesday night or Wednesday. As that happens we could see some light snow, but timing for snow leads to low overall confidence on nailing down precipitation in 6 hour increments. We will leave precipitation chances at less than 20 percent for now from next week. Highs on Wednesday and Thursday look to be in the mid 30s to lower 40s. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 512 PM CST Thu Feb 18 2021 VFR conditions through the period. There is a small chance of mainly flurries at KOFK 06-09z, and KOMA 08-13z. Believe the snow may stay just north of the KLNK site. Maybe only about 0.1 accumulation expected. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Miller AVIATION...DeWald
Area Forecast Discussion
National Weather Service Mount Holly NJ
959 PM EST Thu Feb 18 2021 .SYNOPSIS... A couple of low pressure systems will track northeastward along a frontal boundary located offshore of the east coast tonight through Friday. High pressure approaches the area from the southwest Friday night through Saturday, before building over the Mid Atlantic region Saturday night into Sunday. This high will build offshore Sunday night in advance of our next storm system expected Monday into Monday night. High pressure builds across the southern states with a couple of disturbances possibly affecting the Mid Atlantic region. && .NEAR TERM /THROUGH FRIDAY/... Mid level dry air has moved into the region especially in the 700-500mb layer which caused a loss of cloud ice this evening which is confirmed by the 00z soundings at IAD and OKX. With the loss of mid level RH, steady precip has come to an end however, PW in the low levels is still rather high, and based on RAP low level data there does appear to be at least enough lift and warm air advection to allow for patchy drizzle across the region. With this evenings 00z soundings from both IAD and OKX indicating quite a bit of low level moisture and little in the way of ice nucleation, patchy freezing drizzle has been consistent through the evening and I anticipate that will continue through periods of the overnight hours with accumulations of up to another tenth possible. Previous discussion...Impressive sloped ascent from this morning has translated offshore this afternoon, leaving freezing rain/ rain/ sleet/ and snow in its wake. The threat for snow across DE/ southern NJ and southern PA looks pretty low as mid- level dry air comes in from the southwest. This can be seen pretty clearly on WV. Low level 925 MB flow continues to veer from the southeast this evening. This upslope flow has allowed for reflectivity to again blossom across the Lehigh Valley and Poconos. Most of the precipitation overnight from the upslope flow will be very light in nature, but this light frozen precipitation will make for slippery road conditions. Given this, we have converted the Winter Storm Warning over to a Winter Weather Advisory for all zones. Overnight tonight, temperatures will fall only slightly with widespread cloud cover and southeasterly low level flow. The main story will be an area of low pressure in the low levels that looks to try and organize. At 250 MB the upper level jet streak is actually forecast to strengthen late tonight/ early Friday morning. In the mid-levels, impressive height falls are forecast as the main mid-level wave approaches from the west. Guidance is split here on the location of the development of precipitation in response to the weak surface cyclogenesis. Confidence here on the location of the precipitation is low as guidance is all over the place. Some models are showing the precipitation spreading up near the I-95 corridor, while other guidance is showing precipitation spreading northeast offshore. Given the weak lift described above, have gone ahead and extended the Winter Weather Advisory out to 21z and 00z Friday/ Saturday respectively. Precipitation type with this next system will again be a mix, with snow across the northwestern zones and a snow/sleet/ rain mix across the coastal plain of NJ. Highs Friday afternoon will be in the low to mid 30s with skies remaining overcast. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... Quieter conditions are expected over the weekend, although it will not have a completely dry forecast through Saturday. As an area of low pressure continues to move to the northeast Friday night along a frontal boundary located offshore of the east coast, there could remain some lingering snow showers across eastern Pennsylvania and New Jersey, although the chances are pretty small. Most everyone will be precipitation free however. On Saturday, most areas will be precipitation free, but a steady northwest flow will be in place across the region as low pressure will be located to our northeast and high pressure builds to our southwest. Wind gusts of 20-25 mph can be expected through the day across the area. There will also be a chance of snow showers or flurries for portions of northeast Pennsylvania and northern New Jersey as low-mid level lapse rates increase along with an increase in moisture as well. As a short wave/vorticity impulse moves across the area later in the day, snow showers/flurries could develop for portions of the area. High pressure continues to build into the region Saturday night, and centers itself across the Mid Atlantic region on Sunday. Dry but cool conditions will prevail Saturday night through Sunday. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... The first half of Sunday night will remain dry, however a warm front may lift northward across the area late in the night which could combine with a short wave/vorticity impulse lifting across the area to create some light snow across the area. A frontal boundary is expected to move across the area on Monday, while a triple point low could also develop along the front and move across the area. Temperatures will be cold enough for some area to see snow, but this will be dependent on the track of the developing low. While many areas may begin as snow, a lot of places will likely change over to rain before ending Monday evening. For the Tuesday through Thursday period, high pressure is forecast to build across the southern states. Meanwhile, several disturbances could move across the area Mid Atlantic region each day. Tuesday, and especially Thursday when a more well defined frontal boundary and increase in moisture, have the best chances of precipitation. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight... Now that much of the steady and heavy precipitation has ended, a period of lighter precip and low clouds will prevail across the area tonight. Much of the time, CIGS will be IFR or LIFR, but some periods of MVFR are possible for the NW sites. Light drizzle or freezing drizzle are possible from time to time. NE winds will be around 10 knots overnight. Friday... Low clouds will continue for many areas, some breaks are possible N/W. It`s a rather low confid fcst with low pressure and precip moving northward along the coast. For the most part IFR/MVFR will prevail across the area. Some improvement possible late. N winds 5 to 10 knots. Outlook... Friday night...MVFR or IFR conditions are likely to start off the evening, before improving to VFR overnight. West to northwest winds 5-10 knots. Saturday...Mostly VFR, ceilings may briefly lower to MVFR during the day. Northwest winds 10-15 knots, with gusts 20-25 knots. Saturday night-Sunday...VFR conditions expected. West to northwest winds 5-10 knots, shifting to southwest and diminishing later Sunday. Sunday night...VFR conditions are expected to start the night, before potentially lowering MVFR overnight. South winds around 5-10 knots. Monday...MVFR or IFR conditions likely with a period of rain or snow. South to southwest winds 5-10 knots, with gusts of 15-20 knots possible. Monday night...MVFR or IFR conditions likely to begin the evening, before improving to VFR overnight. Tuesday...Mostly VFR, ceilings may briefly lower to MVFR during the day. West to southwest winds 5-10 knots, with gusts 15-20 knots. && .MARINE... Low pressure will translate northeast this afternoon with northeast wind 20 to 25 knots, with gusts of 25 to 30 knots on our coastal waters through tonight. The wind is forecast to diminish slowly on Friday as it backs to the north behind another area of low pressure. A Small Craft Advisory remains in effect for our ocean waters until 6:00 PM Friday, and for Delaware Bay until 6:00 AM Friday. The Small Craft Advisory for the Atlantic Ocean waters continues through Friday evening. OUTLOOK... Friday night...Small Craft Advisory has been extended through Friday night. Saturday-Saturday night...Winds and waves likely to remain above advisory levels through Saturday night before lowering overnight. Sunday-Sunday night...Conditions likely to remain below advisory levels through Sunday night, although winds may gust around 20 knots at times. Monday-Tuesday...Conditions may remain near advisory levels with seas near 5 feet and winds gusting near 25 knots at times. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Winter Weather Advisory until 7 PM EST Friday for PAZ055-062- 070-071-104>106. Winter Weather Advisory until 4 PM EST Friday for PAZ054-060- 061-101>103. NJ...Winter Weather Advisory until 7 PM EST Friday for NJZ001- 007>010-012>023-026-027. DE...Winter Weather Advisory until 7 PM EST Friday for DEZ001>003. MD...Winter Weather Advisory until 7 PM EST Friday for MDZ012-015- 019-020. MARINE...Small Craft Advisory until 6 AM EST Saturday for ANZ450>455. Small Craft Advisory until 6 AM EST Friday for ANZ430-431. && $$ Synopsis...Robertson Near Term...Deal/Haines Short Term...Robertson Long Term...Robertson Aviation...Haines/Robertson Marine...Haines/Robertson