Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/26/20

Area Forecast Discussion
National Weather Service Birmingham AL
621 PM CST Wed Nov 25 2020 .UPDATE... For 00Z Aviation. && .SHORT TERM... /Updated at 0536 PM CST Wed Nov 25 2020/ Features. Aloft. A deep trough was analyzed by multichannel satellite imagery over Eastern Illinois and Western Indiana. The trough will continue moving northeast toward the Great Lakes Region tonight. GOES-R satellite derived winds show cloud layer winds from 50-70 kt across our Eastern and Central Counties. Surface. The surface cold front now extends from West-Central Tennessee through Central Mississippi. A prefrontal trough now extends to the east of our area from Western Georgia southwest into South Alabama. Southeast. Showers with an occasional thunderstorm continue to affect our East-Central and Southeast counties, generally form Chambers County to Montgomery County and to the south and east. The cold pool from ongoing convection has cleared Pike and Barbour Counties and the heavier activity to the south and west is continuing to weaken with time as it moves into our far southeast counties. Expect showers with a few storms through late evening. Potential for any strong storms is minimal due to the weak instability. Most high-resolution guidance continues to insist on initiating a few showers that may grow into a line of showers with a few storms across the Northwest through the evening. So far, satellite and radar displays have remained fairly quiet so far. There are a few faint echoes from KGWX near the vicinity of the front. Can not rule out a few low-topped showers as surface convergence fields from observational data have improved a bit across Eastern Mississippi over the past hour. The lack of instability, especially with increasing shear and helicity values will be the primary detriment to more widespread development. The further increases in wind shear overnight will require more robust updrafts to sustain convection. While a thunderstorm or two can not be fully ruled out, the potential remains quite low due to poor low-level instability. 05 Previous short-term discussion: /Updated at 1023 AM CST Wed Nov 25 2020/ Through Tomorrow. Weak squall line currently moving across much of the state will effectively act to dampen the instability recovery that was expected for later this afternoon. Numerical models have been slow to pick up on this, although the later HRRR runs are starting to initialize a bit better, showing a progressively weaker recovery with the secondary line formation. Being that this is where the severe weather threat was expected, it is looking less and less likely with time. The shear vectors are decent, especially in the northern CWA, so we will continue to monitor the marginal instability profiles through the remainder of the afternoon and early evening. 17/KLAWS .LONG TERM... /Updated at 0149 PM CST Wed Nov 25 2020/ The long term forecast continues to trend colder at the first part of next week as a deep upper low sets up over the Ohio Valley and initiates a strong CAA regime over the Deep South. There are some signals that moisture may wrap around the low Monday night into Tuesday morning with temps dropping into the 20s across the area. We`ll need to watch this closely for the potential for light, wintry precip across northern Alabama, but until we see more run to run consistency and model agreement, will hold off on mentionable PoPs for now. 86 Previous long-term discussion: /Updated at 359 AM CST Wed Nov 25 2020/ Thursday night through Tuesday. The frontal boundary is stalled across Central AL and becomes more diffuse, but still present. Lingering showers along the front can be expected across the southernmost portions of our area Thursday night. Rain should subside briefly Friday morning as slight ridging slides across Central AL before our next shortwave approaches from the west Friday afternoon and evening. Synoptically, an upper level low pressure system becomes cut-off over the Desert Southwest. The timing of this second shortwave is uncertain, which means it`s difficult to know exactly how long of a break in the rain we`ll see on Friday morning, but by the afternoon to evening hours, we should see numerous to widespread showers generally south of I-20. There could be a few thunderstorms, but instability is lacking overall, so I`ve only added mention for isolated thunderstorm coverage. The cut-off low builds eastward over the Central Plains on Saturday, leading to slight amplification of a ridge over the Gulf States. This will likely lead to another break in the shower/thunderstorm activity over most of Central AL through the day on Saturday. I`ve kept lower PoPs in the forecast for our far southern counties due to the timing differences in these shortwave passages. Rain chances increase substantially on Sunday as the cut-off low slowly becomes phased with the upper trough and lifts eastward through the Ozarks and Mid-MS Valley. Guidance suggests a surface low could develop around this time and push a cold front through our area during the day on Sunday. Due to the numerous rounds of rain that move through just prior to this, it will be very difficult for the atmosphere to destabilize, so I`ve largely removed any mention of thunderstorms with the activity on Sunday. A secondary upper level low pressure system drops southward from Canada through the Upper Midwest Sunday afternoon through evening. This low quickly deepens, pulling in a much colder air mass southward along with it. Right now, the cold front and low pressure system should push to our east Monday morning, meaning the cold air will advect into Central AL through the day on Monday. Because of this, we`ll likely see temperatures drop during the day. The upper level low continues to strengthen over the Great Lakes region, becoming occluded, but will continue pulling in cold air advection into Central AL for most of the day on Tuesday. Low temperatures Tuesday morning and again Tuesday night/Wednesday morning could be in the 20s for most of Central Alabama. As a couple of examples, probabilistic guidance shows around a 70% chance Birmingham drops below 30 degrees Tuesday morning, and increases to an 80% chance for Tuesday night/Wednesday morning. Montgomery is showing an 80% chance for Tuesday morning and a 90% chance by Tuesday night. 25/Owen && .AVIATION... 00Z TAF Discussion. Prefrontal band of showers and isolated thunderstorms still impacting TOI will exit the southeast counties over the next couple hours. Models are still showing some redevelopment ahead of the cold front, but radar and satellite would indicate otherwise. Believe development, if any, will be in the form of a thin line of showers that will slowly push east-southeastward across the area overnight. Included some -SHRA to account for this possible scenario, but this may have to be removed if current trends continue. Ceilings will lower to MVFR at all sites by Midnight. Some northern terminals may flirt with IFR conditions, but IFR is more likely across the south later on tonight. Conditions will gradually improve Thursday afternoon. Southerly winds will become west-northwesterly after frontal passage. 19 && .FIRE WEATHER... Rain chances increase today as a cold front pushes into our area. Expect winds to increase along and ahead of the front as well, shifting from the south to west-northwest as the front passes. There could be a few thunderstorms with this system, but they will likely remain more isolated. The frontal boundary stalls across the area tonight and into Thursday, leading to at least isolated to scattered showers across the southern portions of Central AL Thursday through Friday. The wet pattern should continue through the weekend with a few brief breaks in the rain. Much cooler and drier air builds in for the first part of next week. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 55 69 41 69 47 / 60 0 10 20 40 Anniston 59 71 46 72 52 / 60 10 10 20 50 Birmingham 55 69 47 70 50 / 60 10 10 30 40 Tuscaloosa 52 70 47 71 50 / 50 10 10 50 50 Calera 57 69 48 70 52 / 60 10 10 40 50 Auburn 64 72 55 72 56 / 50 30 20 30 60 Montgomery 65 75 56 75 58 / 40 30 20 40 60 Troy 67 77 61 75 60 / 60 30 20 40 60 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$
Area Forecast Discussion
National Weather Service Grand Rapids MI
1038 PM EST Wed Nov 25 2020 LATEST UPDATE... Update .SYNOPSIS... Issued at 250 PM EST Wed Nov 25 2020 - Areas of fog expanding tonight, lingering into Thursday - Cloudy for Thanksgiving, then sun returns this weekend - Possible wintry weather early next week && .UPDATE... Issued at 1036 PM EST Wed Nov 25 2020 After talking with IWX and DTX I have changed my mind and will go with the dense fog advisory into the early morning hours of Thanksgiving. If the fog lifts behind the cold front, then the midnight shift can cancel it as needed. UPDATE Issued at 946 PM EST Wed Nov 25 2020 The issue this evening is dense fog. Nearly all of our southwest Michigan observation points have visibilities under 3 miles and Kalamazoo is now 1/4 mile in dense fog. MOP is 1/2 mile, LAN is 3/4 mile, here at our office we have between 1/2 and 1 1/2 miles in fog. Normally given the idea fog is moving in so early in the evening and that we already have a fog advisory over our northern CWA it would seem good to expand the fog advisory. However, there is a major glitch. We have a cold front currently crossing Lake Michigan (as seen by the showers on radar, surface pressure rises falling dew points and increased surface pressure gradient. So, I am thinking fog will continue to expand over most of our CWA until the 01 EST to 03 EST time frame. This idea of the fog expanding then going away is well supported by RAP and SREF visibility forecast and related mos products. Then as the frontal boundary crosses the CWA winds will increase as they go from northeast to west northwest and that will clear up the fog issue. It would seem the would be to short a time frame to expand our advisory. So, my bottom line to all of this is I will not issue a dense fog advisory but will have in our grids and issue some social media products that suggest the fog early tonight over the southern and central CWA. && .DISCUSSION...(This evening through next Wednesday) Issued at 250 PM EST Wed Nov 25 2020 -- Areas of fog expanding tonight, lingering into Thursday -- The area of low pressure across central Illinois this afternoon will be weakening / occluding as it moves east. Lower Michigan will remain on the north side of low with rain showers pivoting into the region through this evening before departing. However, in the wake of the showers and as the low edges into extreme southern Lower Michigan, winds lighten amidst abundant low level moisture per latest RAP soundings and some fog will redevelop or expand where it currently exists. A blend of high resolution models suggests the most likely area would be north of I-96 and east of US 131 tonight and tomorrow morning. -- Cloudy for Thanksgiving, then sun returns this weekend -- Low level moisture only slowly erodes on Thanksgiving so clouds will dominate the day. GFS 925mb RH is shown to be around 100% through 21z. It is possible we could see some peeks of sun late. Low level moisture sneaks back in Friday as a shortwave approaches aloft, so clouds will continue to be featured though sun should filter in at times. Much better prospects for sun exist Saturday into Sunday. -- Possible wintry weather early next week -- Projecting the location and intensity of phased systems is a vexing issue, and next week is no exception. A trough is currently moving into the Pacific Northwest region and models are coming into agreement that the southern portion of the trough will detach and become an upper low cutoff over the Four Corners region. This upper low is forecast to migrate east over the Rockies before attempting to phase with a secondary, digging trough over the Midwest and Great Lakes region. Where this phasing occurs will determine if we get significant snowfall or not. Not surprisingly, current long range guidance continues to feature spread with where the upper level phasing induces low level cyclogenesis. A probabilistic approach based on ensemble data indicates more members are favoring cyclogenesis across the lower Ohio Valley or Appalachians Monday into Tuesday, as opposed to the Great Lakes. However, depending on how intense the upper level phasing is, a negatively tilted upper low could substantially pivot and deepen the surface low toward the north/northwest, potentially impacting Lower Michigan. That scenario is supported by some ECE members though most others prefer an Appalachian/East Coast track. The GEFS and CMC members favor the Appalachian track as well. Let`s suppose the scenario occurs where a deep/intense phasing of the systems near the Great Lakes induces a deep surface low across northern OH / southeast MI. Current and past runs of the ECMWF/GEM would support double digit snow totals (spread out over a couple days) across much of the region, which would make this the first significant winter storm to impact Michigan this season. However, assuming the phasing occurs across the Appalachians (ECE, GFS, GEFS, CMC), we see only minor snowfall, or perhaps none at all. Current odds are tilted in this direction but it is obviously something we are watching closely given the higher impacts that could potentially occur. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 642 PM EST Wed Nov 25 2020 Expect for MKG (MVFR), all of our TAF sites are IFR this evening. Winds will remain light through the night. The precipitation has become more showers now than a steady rain, which it was during the afternoon. The rain should come to an end totally by midnight or so. That will allow dense fog to develop over many areas. The most persistent fog will be over area north of M-20 where there is still some snow on the ground. Even so, most of the inland TAF sites are likely to have some dense fog after midnight. As the system moves out on Thanksgiving Day, north winds behind the system should be enough to mix out the fog. Low clouds (IFR becoming MVFR in the afternoon) may last into mid afternoon over western sections and through the evening over eastern sections. && .MARINE... Issued at 250 PM EST Wed Nov 25 2020 Waves will consistently be in the 1-3 ft or 2-4 ft range now through the weekend, so nothing dangerous for small craft. Potential exists for more substantial waves early next week depending on a storm track. Waves of 6-10 ft are not out of the question. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Dense Fog Advisory until 5 AM EST Thursday for MIZ056>059- 064>067-071>074. Dense Fog Advisory until 9 AM EST Thursday for MIZ038>040- 044>046-051-052. LM...None. && $$ UPDATE...WDM SYNOPSIS...Hoving DISCUSSION...Hoving AVIATION...WDM MARINE...Hoving
Area Forecast Discussion
National Weather Service Huntsville AL
905 PM CST Wed Nov 25 2020 .NEAR TERM...(Tonight) Issued at 905 PM CST Wed Nov 25 2020 A cold front was gradually moving eastward across the Tennessee Valley. It was moving slower than previously thought,, currently extending from east of Nashville, to near Muscle Shoals and the MS Golden Triangle. Winds west of it have shifted to a westerly direction, gusty in the 5-15 mph first, then subsiding to around 5kt. Another item adding to the mix is a pooling of moisture over NE Alabama. This moisture upgliding in the 300-305K region was producing showers over parts of far southern Marshall and Dekalb AL counties. No thunder has been reported, but given graupel in the ~15 Kft ASL, could not rule out a rumble or two over the next couple of hours. Otherwise, this shower activity should end from west to east over NE AL this evening. The cold front per timing from the NAM and RAP should the NE AL/NW GA border around midnight, being pushed by high pressure building in from the Southeast Plains. The high moving ever closer in the overnight will result in winds becoming light/variable. This plus clearing skies and residual moisture from recent rainfall could produce fog formation before sunrise Thanksgiving Day. Overnight low temperatures should cool into the 40s (near 40 NW AL, to upper 40s NE AL). .SHORT TERM...(Thursday through Friday) Issued at 253 PM CST Wed Nov 25 2020 On Thursday, the high pressure cell will move into KY and TN, with temperatures warming into the lower to middle 60s. Fog is again possible Thursday night into early Friday morning. On Friday, warm advection/isentropic ascent may induce clouds that lift northeast through the afternoon hours, with light rain possible in our southwest counties. But at this time, will leave the forecast dry. Highs should still reach the middle to upper 60s. A cold front will drop southeast through the Ozarks and mid South, arriving in the TN Valley just after sunset. .LONG TERM...(Friday night through Tuesday) Issued at 253 PM CST Wed Nov 25 2020 This front should continue to push further southeast on Saturday. This should keep shortwave energy and deeper moisture associated with them to the south of the area primarily. Cannot rule out enough forcing and moisture to creep up to locations near and south of the Tennessee River, but this activity should be very isolated in nature. Lows in the lower to mid 40s look reasonable in most locations. The closed upper low moves into eastern Texas Saturday evening. High pressure should remain firmly in place over the Tennessee Valley though, as it`s center shifts into the Mid-Atlantic region. This should help to keep drier air in place over much of northern Alabama and southern middle Tennessee. Abundant cloud cover by midnight or shortly before should help to keep temperatures from dropping much below the upper 30s to lower 40s. During the day on Sunday, the upper low moves east into southern Arkansas and northern Louisiana. Also, most guidance swings a strong longwave trough axis southeast from the Upper Midwest and begins to merge these two pieces of energy. This produces some very strong cyclogenesis and a quickly developing surface low that moves from southern Lousiana northeast into the Carolinas or Ohio Valley by Monday morning. Strong diffluence aloft combined with forcing ahead of this strong upper low could produce a large areas of heavy rainfall over the southeast on Sunday. Models do differ on how quickly the drier air east of the I-65 corridor in northern Alabama is saturated near the ground. At this point, went with an average of the two solutions, since drier air tends to hold on in the east a bit longer than models usually predict. However, still included chance PoP (east) to likely PoP (west) in the forecast. With strong southerly flow expected on Sunday ahead of the surface low, highs despite cloudy conditions should climb into the upper 50s to lower 60s. Most guidance moves the upper low right through northern Alabama and central Tennessee Sunday night into Monday morning, as it tries to phase with the longwave trough axis. ECWMF seems to phase it more and bottoms out the surface low pressure with this system below 990 mb. GFS is not quite as strong with the phasing and deepening of the surface low. Either way, heavy and more widespread rainfall should be the result Sunday night, before tapering off to more scattered coverage on Monday. Right now, guidance really doesn`t show any elevated or surface based instability making it northward into northern Alabama. However, with the strong, deep forcing with this system heavy rainfall of 1 to 3 inches looks possible. Keep total closer to 2 inches in current forecast though. Models differ on how quickly very cold air will move in behind the deepening surface low and attendant cold front Monday night into Tuesday. ECMWF is much quicker with this process and also much deeper with the pressure drop with the surface low as noted earlier. For now, due to the average track of the low being more to the north to northeast with the low in most guidance, went in between. Cloud cover and a TROWAL setup from the east may keep high temperatures in the lower to mid 40s on Monday. However, by Monday night into Tuesday for sure the brunt of the coldest air should push into the area. It looks like the coldest air of the season so far, with lows dropping into the lower to mid 20s Monday night. Could see some light snow or a mix of light rain and snow. Only kept 20 percent chance though at this time. Tuesday looks very cold with highs only climbing into the upper 30s to lower 40s and that may be generous. Winds chills in the forecast starting out in the teens and only climbing into the lower 30s by the afternoon hours look reasonable. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 531 PM CST Wed Nov 25 2020 A cold front was beginning to near NW AL from the west. It should reach KMSL within the next hour or two, KHSV in the 02-04Z timeframe, then be east of the area by 07Z. Forecast models have been consistent in hinting at a redevelopment of showers and maybe a thunderstorm or two over NE AL as lift and better forcing from the front are realized. Shower activity should exit quickly east of the region by local midnight, with VFR weather expected for the rest of the TAF. Winds will slacken significantly overnight. This and clearing skies could make predawn fog formation possible. Did not include it in this issuance given too much uncertainly. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...RSB SHORT TERM...17 LONG TERM...KTW AVIATION...RSB For more information please visit our website at
Area Forecast Discussion
National Weather Service Northern Indiana
844 PM EST Wed Nov 25 2020 .SYNOPSIS... Issued at 658 PM EST Wed Nov 25 2020 Rain showers will continue to lift northeast from central Indiana this evening, with an isolated thunderstorm possible this evening south of US Route 24 across northwest Ohio. Conditions will dry out from west to east overnight. More seasonable weather arrives tonight and the weather becomes quieter for Thanksgiving Thursday through Sunday. && .UPDATE... Issued at 837 PM EST Wed Nov 25 2020 Line of showers with a few embedded storms will continue across southeast portions of the area over the next few hours. Best remaining instability appears to be tied to mid level cold core currently working across northeast Indiana where 01Z RAP analysis depicts 100-200 J/kg of instability. An isolated wind gust to 40 mph will be possible with this weak pocket of instability through 04Z, but otherwise drying conditions overnight with lingering low chances of light rain showers in deformation type forcing. 1006 mb sfc low is entering NE Indiana this evening and while low is not particularly deep, it is a compact feature with respectable pressure rises building in behind from east central Illinois. Progression of this isallobaric forcing will likely result in brief period of 15 to 20 mph gusts across west/southern portions of the area late evening/early overnight. Have issued a marine dense fog advisory for the nearshore waters as inverted sfc trough and accompanying near sfc moisture convergence persists. Focus for this fog should gradually shift east of Lake Michigan after 06Z. && .SHORT TERM...(This Evening through Thursday) Issued at 248 PM EST Wed Nov 25 2020 An upper low over St Louis continues to provide the area with a chance for showers into tonight though the rainfall coverage is expected to be less than the morning`s was. This may provide the area with a chance for thunder as ~200 J/kg MUCAPE and 6.5-7.5 ML Lapse rates move in from the southwest out ahead of the sfc low. Forecast soundings from down south of US-30 this evening indicate a very moist low level of the atmosphere with little to any sfc instability as an inversion appears to be in place. Even still, could see some stronger gusts as storms bring the stronger winds aloft to the surface. Then, the sfc low moves across the area early tonight canceling the steadier rainfall chances from southwest to northeast as it does so. Could also see some drizzle follow the thunder chance this evening though. This ushers in a cooler airmass giving way to more seasonable temperatures starting Thanksgiving and continuing into the weekend. Tonight`s temperatures drop back into the 40s with only a slight diurnal rise back to either side of 50 degrees for highs on Thursday. && .LONG TERM...(Thursday Night through Wednesday) Issued at 248 PM EST Wed Nov 25 2020 Upper ridging and sfc high pressure control the weather from Thanksgiving Thursday through the weekend allowing for quiet weather. Some of the higher res guidance does keep some lower clouds around through Friday so will hang on to cloud cover through most of that period. Temperatures should be seasonable in the 40s to low 50s for highs with lows back below freezing Friday night through the end of the forecast. Well, we had better agreement with the 00z model suite between deterministic and ensemble forecast guidance for the Sunday night into early next week period with that strong low pressure system and then the 12z GFS came in and had to throw that out the window. What models are indicating for this time period is that a cut off upper low traverses across the southern CONUS north of phased upper jets. A second strong shortwave along the northern stream interacts with the developing low pressure system and causes deepening as the low moves north and more upper jet interaction occurs. As we just saw, and is normal for an event like this, there`s still plenty of time for drastic changes between model runs with the main pieces still in the Pacific at this time. The main questions are what track does the low pressure system take as it ventures north out of the southern CONUS because the timing of these two waves are important to get a favorable track for snow here, how far can the moisture get into the area, and what is the extent of the cold air across the area. On the back side, the north/northwest winds may also favor a period of lake effect snow, but the intensity/location of that is obviously uncertain. Check back for continuing forecast updates on this period. && .AVIATION...(For the 00Z TAFS through 00Z Thursday Evening) Issued at 647 PM EST Wed Nov 25 2020 Vigorous upper level vort max continues to progress east-northeast across southern Indiana this evening. This strong forcing has resulted in linear convection developing across primarily central/southern Indiana. Sfc low is entering NW Indiana as of 00Z and should rapidly shift to the western Lake Erie vicinity after midnight. Given this sfc low track, main axis of very weak instability should remain south of terminals as associated cold front tracks through over the next several hours. Thus, will continue to omit thunder. A period of rain is expected, with bulk of this rain affecting KFWA. Areas of fog are possible north of this low track through early overnight, but any lower vsbys should improve late tonight. Deep layer subsidence builds in overnight into Thursday morning, but trapped low level moisture may make improvement slow. Given sfc low track, will maintain more pessimistic cigs/vsbys at KSBN in comparison to KFWA with improvement back to MVFR at both terminals closer to midday period tomorrow. Winds generally to remain at or below 10 knots through this period with the exception being late evening/early overnight as brief isallobaric forcing associated with the sfc low passage provides a period of westerly gusts of 15 to 20 knots. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...Dense Fog Advisory until 4 AM EST Thursday for LMZ043-046. && $$ UPDATE...Marsili SYNOPSIS...Marsili/Roller SHORT TERM...Roller LONG TERM...Roller AVIATION...Marsili Visit us at Follow us on Facebook...Twitter...and YouTube at:
National Weather Service Jackson KY
946 PM EST Wed Nov 25 2020 .UPDATE... Issued at 946 PM EST WED NOV 25 2020 A line of showers are starting to push into eastern Kentucky this evening. This line of showers will bring brief gusty winds of 25 to 35 mph and brief heavy rainfall. Did adjust the grids to better time this line through the area and went closer to the HRRR for this. Also opted to remove thunder mention, since there has been no lightning through the afternoon and evening with any of this activity as it move across the state. All updates complete and sent. UPDATE Issued at 645 PM EST WED NOV 25 2020 A low pressure is working across the Ohio Valley with cold front extending into central Kentucky this evening. There have been a few gusty showers develop along and ahead of the cold front. While the thunder chances look low will leave the mention for now through the evening. Overall these showers will bring brief gusty winds and brief moderate to heavy rainfall. These showers will progress into the far west around 2Z to 3Z and rest of the area between 4Z to 5Z perhaps 6Z in the far east. Updated PoPs and other grids to better reflect the latest obs and trends. Otherwise a fairly minor update overall. && .SHORT TERM...(This evening through Thursday night) Issued at 419 PM EST WED NOV 25 2020 Late this afternoon, an upper level low is moving across IL with a parent sfc low centered across eastern IL and a triple point low over western IN a warm front extending east and a cold front trailing south into western KY. A prefrontal band of showers is working across the region and currently over the eastern counties. Winds have been gusty at times, though gusts have generally diminished to less than 30 mph. Through this evening and tonight, the upper level low is expected to track into Lake Erie with the sfc low also tracking into the Great Lakes. The trailing cold front with the cold front continuing to move east across the Commonwealth this evening and into the early portion of the overnight hours. A general lull in shower activity should occur behind the initial band of showers and ahead of the cold front. A band of showers and potentially a couple of embedded thunderstorms is anticipated along and just ahead of the front based on recent guidance and upstream trends. Some gusty winds are possible with this, potentially into the 30 to 40 mph range. Low clouds are expected to move in behind the front and persist into the day on Thursday as low level moisture wraps into the OH Valley along and in advance of the shortwave trough. With gusty winds starting to wind down the Lake Wind Advisory will be allowed to expire at 5 PM. The shortwave trough axis will move east of the area on Thursday with a shortwave ridge moving into the area late in the day. On Thursday night, the axis of the ridge will move east of the area though sfc high pressure will build into the area. Low level moisture is expected to persist between the 925 mb and 850 mb levels through the end of the period and although dry weather is expected after tonight, low clouds should be persistent. With persistent low clouds, diurnal temperature ranges should be on the small side to end the period. .LONG TERM...(Friday through Wednesday) Issued at 344 PM EST WED NOV 25 2020 We start the weekend Friday with decreasing clouds and dry weather as high pressure maintains control. Temperatures are mild in the upper 50s to low 60s. Ridging moves off east as an upper level trough descends down from the Upper Midwest, supporting the passage of a cold front late Friday night into Saturday. Impacts from this front will be minimal. The trend has been for less and less moisture ahead of this front, so while clouds will be on the increase, the forecast should remain dry and temperatures only take a slight dip. High pressure moves in behind the front, clearing skies and maintaining the dry weather through Saturday. Our next systems is set to impact our area early next week. The upper level trough that supported the cold front over the weekend leaves behind a closed low over the southwestern US. A trough moving through the northern stream, eventually phases in with the southern stream low. This supports a low forming in the southeast, near the gulf coast that then travels up to the northeast, strengthening as it does so. While models have come into more agreement over the broad pattern, there are still some details that are not quite nailed down with regards to timing, strength, and intensity. How these details are realized will dictate the specific impacts felt here. So, have stayed close to blended guidance but acknowledge the possibility for refinement as time moves on. Overall, precip returns to the forecast late Sunday and continues through the first part of the workweek while temperatures take a sharp drop. With the cold air moving in, we could see some snow Monday night into Tuesday with the moisture wrapping around the system, but there is less confidence around the details given how far out it is. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) ISSUED AT 630 PM EST WED NOV 25 2020 The period is starting off VFR as we are in a dry slot across portions of eastern Kentucky. A cold front will push east through the evening and a line of showers and perhaps a rumble of thunder arrive along and near the boundary. This could bring some gusty winds at times and lead to lowering VIS and CIGs briefly. There is an extensive area of stratus wrapping around behind the front and this will lead to lower CIGS in the MVFR range later tonight and through much of the remainder of the period. While we have seen some of winds of 10 to 15 knots with gusts of 25 knots at times early this evening, we will see these subside through the evening before the front arrives. This front could lead to 20 to 25 knot gusts, but again these will be fleeting as low level jet departs and front pushes through. The low level jet and inversion setting up could also lead to some low level wind shear through the evening and into part of the night before the low level jet relents. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...JP LONG TERM...HAS AVIATION...DJ
Area Forecast Discussion...CORRECTED
National Weather Service Chicago/Romeoville, IL
918 PM CST Wed Nov 25 2020 .UPDATE... 916 PM CST The Oz DVN sounding is fairly representative of the airmass across the region, still a deep moist layer in place and warming temperatures with height. A stout low level inversion is evident further upstream at MPX, but the moisture layer is much more shallow, indicative of the subsidence inversion that will eventually works its way our direction now that winds are shifting around to the northwest. One last hurrah with light rain from lower level lift on the back side of the departing stacked low pressure system before more significant height rises go to work on the stratus layer. This cloud deck still extends back to the MN/ND border and also to the IA/NE border where we are starting to see some erosion and thinning of the cloud shield. We should see some clearing through the afternoon on Thanksgiving Day, with the highest probabilities to the west, lower chances in Indiana before "sunset". With the solid stratus in place and increasing wind flow tonight, the dense fog threat is low, though some lighter fog will continue. KMD && .SHORT TERM... 305 PM CST Over the next few hours, a few isolated thunderstorms will remain possible south of I-80, though it appears the threat for lightning is fairly low. Based on recent radar trends, best chance will probably be for Benton County and perhaps extreme southeast Iroquois and far southern Newton and Jasper counties. With the area of steady rain that had been over northern Illinois much of the day now having lifted north into Wisconsin, activity will be of a showery nature in the vicinity of the potent mid/upper level low. Highest coverage will south of I-80 with isolated to scattered showers north ending during the evening. There could also be some drizzle at times as socked in deep moist layer under inversion and departing influence of upper low could yield patchy drizzle. Main concern this evening into Thanksgiving morning is fog potential. Lakefront locations and a few miles inland of the lake are most concerning from a dense fog perspective. Webcams along the shore indicate pretty soupy conditions. With north-northeasterly flow on the backside of the surface low to our south into mid evening, dense fog out over the lake could bleed inland. HRRR and NARRE have consistently been favoring near lake areas for the dense fog threat through the mid to late evening hours. Winds shifting to northwesterly behind the departing surface low may advect fog southeastward toward Indiana, followed by mechanical mixing probably eroding lingering dense fog. Will need to monitor webcam and observational trends closely for possible SPS or even Dense Fog Advisory issuance. With essentially no dry advection and only weak cold advection in the wake of the synoptic system, winds over land fairly light, and the wet conditions the past two days should support patchy fog inland. Signal isn`t as strong for dense fog, probably owing to mechanical mixing from west-northwest winds around 15 kt at 950 mb. Aside from any patchy fog into Thanksgiving morning, there are no additional significant concerns. Main item of note will be how long the extensive low stratus deck under strong subsidence inversion takes to erode. Have continued with more pessimistic trend, which keeps clouds around for most of the daylight hours, especially in northeast IL and northwest Indiana. Strengthening southwest flow aloft could finally advect and erode the stratus during the mid to late afternoon. Given the above, nudged forecast highs downward slightly into the mid to upper 40s, 5 degrees or so above normal. A cold front trailing from low pressure over Hudson Bay will then shift across portions of the area prior to daybreak Friday. Forecast lows are above normal in the lower to mid 30s (upper 30s downtown), with mid and high clouds and steady winds propping temps up. Castro && .LONG TERM... 234 PM CST Friday through Wednesday... The seasonably mild temperatures and dry weather that arrive for Thanksgiving will persist through the weekend before cooler air and increased precipitation chances return for next week. Latest trends suggest temperatures next week will only drop to near or just below normal values for early December, while the best precip chances will be east of the local area. For Friday, the passage of a weak and dry cold front will turn winds northwesterly and in most locations keep highs a bit below values expected for Thursday and the weekend. Overnight lows Friday night also will reflect the cooler and drier air in the ridge that trails the front. On Saturday we recover a bit as the axis of the surface ridge slides east of the area, putting us in the milder southwesterly flow on the back side of the ridge. The continued influence of the ridge as it continues east through the Ohio Valley and into the mid-Atlantic states will again support seasonably mild highs and continued dry conditions Sunday. By early next week the situation becomes more complicated and continues to bear watching as models struggle to decide how to handle an upper low that gets cut off from the northern stream flow late Saturday over the Four Corners region. The deterministic GFS and ECMWF handle this quite differently, though their ensemble solutions are in much better agreement. The question is how far west the surface low may retrograde as it and its upper level counterpart lift out of the northwest Gulf region and get reincorporated into the northern stream. Some solutions continue to show this as far west as Ohio while the ensembles favor more of a mid-Atlantic to New York track. Either way it appears we are in for some strong northerly winds, but a more westerly track would also locally increase precip chances, including periods of snow. The present forecast trends reflect more of the ensemble solutions and only have slight to chance POPs locally, but again these trends will be monitored closely. Regardless of how Monday and Tuesday play out, Wednesday presently looks drier and continued cooler, though again close to seasonable averages. Lenning && .AVIATION... For the 00Z TAFs... Ceilings of 200-300 feet and visibilities at times dropping below 3 miles at ORD/MDW will gradually improve toward 500 feet and 6 miles, respectively, within the first few hours of the TAF period as the low-level flow shifts north/northwesterly shunting off moisture flux from Lake Michigan. Confidence is high that ceilings will then remain somewhat steady at 500-700 feet through the overnight hours at all terminals before rising somewhat to about 1000 feet after daybreak Thursday thanks to modest dry-air advection from the northwest. With a stout low- level inversion in place, opted to continue the pessimistic route and maintain prevailing overcast skies through much of Thursday. Toward 21Z Thursday, an increase in low-level flow atop the inversion associated with an approaching upper-level shortwave trough should encourage enough mixing to afford breaks in the cloud deck, with a non-zero chance for a return to VFR by the very end of the TAF period. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Dense Fog Advisory...nearshore waters until 3 AM Thursday. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at: