Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/23/21

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1203 AM EDT Thu Sep 23 2021 .AVIATION... No big changes to expectations on flight categories late tonight and through the day. The surface low continues backing west from central Lake Erie into SE MI but on a slightly farther north track. This leads to some minor adjustments on wind direction forecasts across the terminal corridor, mainly south of FNT. Otherwise, the last surge of heavy rainfall unfolds for a few hours after midnight and then weakens and shifts into western Lower MI by sunrise. Showers are then replaced by drizzle and fog in the weaker pressure gradient around the surface low center. IFR/LIFR ceiling and mostly IFR visibility becomes widespread across the terminal corridor with just some minor improvement to high end IFR by Thursday evening. For DTW... Northerly wind gusts ease as the surface low moves nearly overhead by early morning. As the low approaches, primarily MVFR conditions drop to IFR with LIFR likely in drizzle, fog, and low clouds. Some improvement occurs by early afternoon as the low drifts north of the terminal area into Thursday evening. .DTW THRESHOLD PROBABILITIES... * High for ceiling 5000 feet or less through the period. * Moderate for ceiling 200 feet and/or visibility 1/2 SM late tonight until early afternoon. && .PREV DISCUSSION... Issued at 1023 PM EDT Wed Sep 22 2021 UPDATE... One final phase of this rain event keeps the Flood Watch going tonight while the strong surface low in central Lake Erie has the peak of the wind event in progress. The Flood Watch and Wind Advisory/Warning continue through tonight with expiration times remaining on schedule as conditions improve early in the morning. A relative break in rain activity occurred during the evening between the primary moisture axis and the deformation/trowal within the upper low. This provided a welcome breather for run-off to occur before the next batch of showers moving in from IN/OH at press time. Observations support model guidance that indicates the upper low has plenty of moisture and dynamics to wring out another 1 to 2 inches of rain during the night before closing and pinching off the moisture axis mid to late morning. The wind was the other high impact aspect of this event which really got going along the Lake Huron shoreline early to mid evening. The latest runs of RAP model soundings indicate a well mixed boundary layer up to 850 mb at points along the shoreline as of 00Z which continue 50 knot potential through nearly 06Z before diminishing as the low backs into SE Michigan during early morning. PREV DISCUSSION... Issued at 339 PM EDT Wed Sep 22 2021 DISCUSSION... A Flood Watch remains in effect for most of Southeastern Michigan through tonight. A Wind Advisory and Lakeshore Flood Advisory also remain in place from parts of the Saginaw Valley into the Thumb where strong onshore flow will persist (and further strengthen) into tonight. Rain continues to stream northward through the area this afternoon within an area of very strong upper level divergence as upper vort lobe lifts into the area in advance of deepening upper low pressure over Indiana. Expect periods of light to moderate rain to prevail into the early evening hours with some pockets of heavy rain likely as well as moisture plume feeding around this developing system remains impressive. Meanwhile, surface cyclo-genesis is ongoing over central/eastern Ohio in advance of main upper system. This low pressure will strengthen into tonight and pull back northwest into far western Lake Erie/far SE Lower Michigan as upper low deepens considerably as strong jet (80 kts at H5/100+ at H3) pivots northeast into the region around its base. This process will lead to a strong increase in FGEN forcing which will pivot north/northwest into the region later this evening into the overnight. Upper level divergence will remain in place to further enhance lift and pockets of elevated instability will also ride back NNW up the frontal slope over the region as this system quickly matures. All of these factors favor a continuation of rain, heavy at times, after perhaps just a brief lull early this evening between this afternoon`s vorticity lobe and the main system tonight. In fact, would expect rainfall rates to increase as the strongest forcing/lift develop over the region late this evening into parts of the overnight. Convective elements within the rain shield will also aid in higher rates during this period of time. Additional rainfall of 1 to locally 2 inches will be likely from late today into tonight. As the deepening surface cyclone pivots back towards the area, expect a tightening pressure gradient as well with very gusty north to northeast winds. This will be especially true downwind of Lake Huron where a Wind Advisory will remain in effect through tonight as wind gusts to 45 to 50 mph are expected along/near the shoreline. These strong onshore winds will also lead to some lakeshore flooding and erosion concerns with a Lakeshore Flood Advisory also remaining in place through tonight. Further inland, wind gusts of 30 to 40 mph will be common over much of the rest of the forecast area. As the upper system matures/occludes tonight as it lifts north over the region, mid level dry air will work into the system and lead to a steady downtrend in rainfall rates/coverage later tonight into early Thursday morning. That said, periods of rain will persist into/through Thursday as the low pressure, basically vertically stacked to 150 mb, lifts gradually north/northeast across the region. After a cool day in the 50s again Thursday, transient shortwave ridging will work into the area on Friday and bring dry conditions will high temperatures back to near 70. A vigorous shortwave and attending cold front will then surge through the area late Friday night into Saturday. This will bring the chance of scattered showers and cooler conditions back into the 60s Saturday with cooler conditions then persisting into Sunday before heights gradually build early next week on the southwest periphery of upper troughing over eastern Canada. This should allow 70s to return to the forecast for the Monday/Tuesday time frame for at least portions of the area. MARINE... Low pressure continues north this evening preserving a constricted pressure gradient. Numerous surface obs are currently gusting to gales, and some sustained gales are expected upon arrival of the strongest gradient winds late this evening. Upped peak gusts by a couple knots based on latest guidance, but still comfortably below storms (50 knots) across the central Great Lakes. Also made minor timing adjustments to the Gale Warning, ending earlier (2 AM EDT) for western Lake Erie and Lake St. Clair since the strongest winds should clear north shortly after midnight. Gales are still marginal for northern Huron, but the southern fringe of the zone should see a period of even gales, thus kept the northern most marine zone in with this update. Otherwise, the current headline remains on-track. Occasional waves peak near 20 feet late tonight, mainly for the south-central Huron basin. Winds drop-off quickly mid-morning Thursday, but residual wave energy will likely warrant a back-end Small Craft Advisory for the southern Huron nearshores until the afternoon. Weaker yet modest W/SW winds expected behind the low through the weekend. HYDROLOGY... Periods of rain will continue as an upper low pressure deepens to the southwest. As this storm system lifts into the region tonight, expect areas of heavy rain to become more common this evening with this activity persisting into part of the overnight. An embedded rumble of thunder or two can also be expected. Additional rainfall by early Thursday morning should average generally around one inch with local 2 inch amounts possible. This rainfall will compound flooding on area rivers that is already underway due to the heavy rainfall that has fallen to this point. Some areas of urban and poor drainage flooding can also be expected with the most notable flooding within the drainage basins of the various branches of the Clinton and Rouge Rivers && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Flood Watch until 8 AM EDT Thursday for MIZ049-053>055-060>063- 068>070-075-076-082-083. High Wind Warning until 8 AM EDT Thursday for MIZ049-055-063. Lakeshore Flood Advisory until 8 AM EDT Thursday for MIZ048-049-054- 055-063. Wind Advisory until 8 AM EDT Thursday for MIZ048-054. Lake Huron...Gale Warning until 8 AM EDT Thursday for LHZ361>363-421-422-462>464. Storm Warning until 8 AM EDT Thursday for LHZ441>443. Lake St Clair...Gale Warning until 2 AM EDT Thursday for LCZ460. Michigan waters of Lake Erie...Gale Warning until 2 AM EDT Thursday for LEZ444. && $$ AVIATION.....BT UPDATE.......BT DISCUSSION...DG MARINE.......KK HYDROLOGY....DG You can obtain your latest National Weather Service forecasts online at
Area Forecast Discussion
National Weather Service Gray ME
1133 PM EDT Wed Sep 22 2021 .SYNOPSIS... Warm and humid conditions will persist across the region through the end of the week as southerly winds continue ahead of a slow moving cold front. This front will cross the region late Friday and into Saturday with a period of widespread rainfall likely along with a few thunderstorms. Improving conditions are expected by the second half of the weekend as drier air arrives from the west. A cold front will then approach the region early next week with another threat for showers. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Update... Will continue with the chance of showers or patchy light rain across the region late this evening, mainly over New Hampshire where persistent echoes continue to enter the state per latest radar imagery. Some light precipitation will continue in the mountains and foothills of Maine as well. Made minor adjustments to current temperatures, dew points and winds. Some patchy drizzle and fog will continue to form after midnight per latest HREF and HRRR solutions and observational trends. Prev Disc... High Impact Weather Potential: Patchy dense fog is possible tonight. Pattern: The trough/ridge pattern across central/eastern North America has slowly shifted east over the past few days with the longwave trough axis now moving into the Great Lakes region with the downstream ridge now just east of the US East Coast. Between these two features is a deep plume of moisture...evident on water vapor imagery...streaming north from the Gulf of Mexico up along the Appalachians west of New England. In our area...a prolonged period of southerly flow has yielded a large amount of stratus...along with some drizzle and fog along with a few rain showers. More of the same is expected through tonight with little change to the overall flow configuration. Thus...forecast challenges center on the evolution of fog/stratus and whether we`ll see any dense fog across the forecast area. Through this evening: Weak vort lobe in the southerly flow aloft has brought a modest increase in shower coverage over New Hampshire this afternoon. These will continue to lift north and weaken through the evening leaving us with ample low cloudiness that will thicken for all but far northern areas. It will remain mild...with 8pm temperatures still in the 60s throughout the CWA. Tonight: No real change to the pattern through tonight with a repeat of low clouds...drizzle...and some fog expected from the mountains south. Short range guidance paints another weak band of enhanced vorticity aloft pushing north and west through the forecast area overnight. This may help to bring a few more showers...otherwise the best chance for shower activity will remain along the southern slopes of the mountains. Higher dewpoints than 24 hours ago suggests that we`ll see more in the way of fog...with locally dense fog possible with the strongest signal for this being over the foothills. Given the continued moisture advection...expect lows to take another step upward with upper 50s in the mountains and lower 60s to the south. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... High Impact Weather Potential: Additional patchy dense fog possible Thursday night. Pattern: A potent shortwave dropping into the Northern Plains will act to take the trough/cutoff low to our west and kick it north...with little room to move downstream given a high over low /Rex block/ setup just off the east coast. Through the short term forecast period the well as the collocated occluded surface low will move north from a position near Detroit Thursday morning to a position over Georgian Bay by Friday morning. East of this...a slowly advancing cold front associated with an atmospheric river will slowly march east...nearing our forecast area by the very end of the short term period. With moist...southerly flow continuing ahead of this advancing cold front forecast concerns will continue to be centered on fog...stratus...drizzle...and the potential for showers. Thursday: H5 555DM low will slowly move north through Michigan during the day out with a 590DM high centered just south of Nova Scotia. Warm/moist southerly flow will continue with T9s sitting around the +17C mark with PWATs still not all that impressive /nearing 1"/ given deep dry wedge overtopping the surface-based moist layer. Like today...expect we/ll see improving visibilities and ceilings during the day...but another mostly cloudy day is expected with some showers in the mountains given upslope flow. Temperatures aloft really won/t be that different than 24 hours expect 70s to dominate again. Thursday Night: There is rather strong ensemble agreement that the frontal boundary will remain west of the CT Valley through daybreak Friday which means the potential for any heavier rainfall will hold off until the beginning of the long term forecast. The southerly/ southeasterly low level jet will gradually strengthen overnight which...given continued moist upslope should allow for the upslope showers in the mountains. Still...the moisture looks to be relatively shallow...perhaps 5kft...with a robust dry wedge above this with impressively high heights at H5...nearing the 99th percentile for this time of year. Statistical guidance is a bit more robust with the fog during this period than the previous night...but there is little support for widespread dense fog and will therefore just continue patchy fog mention...particularly over coastal ME into the foothills given the best marine influence. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Starting with a global view we`ll have a higher amplitude and blockier pattern developing over North America as the colder polar air starts its seasonal slip southward. By the end of the week an upper level low over the Great Lakes will begin to cut off while high pressure noses east of us into the Gulf of St. Lawrence. These two features will provide the alignment for a feed of southerly moisture to start the weekend. By the end of the weekend, expect there to be some progression with the low pulling north and a more open wave developing. This should allow systems to continue to remain progressive through the start of next week. Focus of this forecast will be the Friday-Saturday time frame. Here a surface low will occlude over the Great Lakes with an extended warm sector out ahead of it. The cold front will serve to focus the southerly flow of moisture into the region, setting us up for at Atmospheric river with heavy rainfall possible. At this point the timing of this system is relatively secure, with all the major deterministic and ensembles showing a period of rain from Friday morning through to Saturday night. This agreement is reflected in the high PoPs issued with this package. Rainfall amounts are a bit sticker. Southerly flow and PWAT values of over 1.6" result in net moisture transport of > 750 which is enough to be considered an `atmospheric river`. With the system wrapping up tend to favor a slightly more conservative take on the total QPF, so while there are a few extreme options out there feel sticking closer to the mean is more reasonable. Thunderstorms will also be a threat Friday afternoon. Forecast soundings show significant low level instability with CAPE upwards of 1000 J/kg. Additionally there is a 40kts low level jet which will provide for plenty of shear and turning hodographs. Along the ME coast, saturated low levels will keep things in the fog with only elevated convection, however across New Hampshire thunder is likely as the front moves through and have included this in my grids. The same low level jet which will increase the shear will also allow for training of thunderstorms along the front which could make for locally higher rainfall. By Saturday the consensus is leaning towards precipitation departing the region and have kept PoPs a bit lower through evening, although some showers are likely to linger. The low pressure aloft will linger to our west with another system moving through late in the weekend. Here timing differences start to appear amongst the guidance with the GFS favoring a more progressive solution and the Euro and CMC lagging behind. Have slightly favored the slower solution here which keeps the upper low overhead and showers in the area, especially the mountains through the start of next week. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... Short Term... Summary: Moist southerly flow will cause an extended period of low clouds...fog...and some drizzle that will continue through Thursday night with some improvement each afternoon. Restrictions: Conditions improving to VFR/MVFR attm but showers are moving north toward southern New Hampshire which...will begin to bring deteriorating conditions here...with further deterioration to LIFR/IFR tonight /outside of HIE/ as stratus re-solidifies and fog/drizzle develop. Expect this cycle to occur again on Thursday with improving conditions during the day before another round of LIFR/IFR Thursday night with conditions possibly even a bit worse Thursday night than tonight. Winds: Southerly winds are strengthening to around 10kts inland and 10g18kts along the coast. These will diminish to less than 5kts overnight before increasing to around 10kts with some higher gusts from the southeast for the day on Thursday. 5-10kt southeasterly winds are expected to continue Thursday night. Lightning: Lightning is not expected through Thursday night. Low Level Wind Shear / LLWS: No LLWS is expected through Thursday. Thursday night...low level southeasterly winds will increase with a period of LLWS likely. Long Term... High impact weather potential for Friday. Along the Maine coast IFR with fog and low stratus will likely linger through most of the day. Further east across New Hampshire clearing will allow for instability to develop and thunderstorms with heavy rain will cross the area from west to east impacting all portions of the CWA. Additionally a low level jet may result in a brief period of low level wind shear as the front moves through. By Saturday conditions will improve with just lingering MVFR showers through the weekend. && .MARINE... Short Term...Wind gusts have pushed towards 20kts this afternoon from the southeast...but are expected to diminish some this evening. Expect marine fog to be on the increase tonight through Thursday as surface dewpoints rise...with continued southerly winds bringing gradually increasing wave heights. Winds and waves begin to approach SCA levels as this forecast period ends Thursday night. Long Term... Southerly flow will increase on Wednesday ahead of a cold front crossing the Gulf of Maine and a few gusts to SCA levels are possible. The front will clear through on Saturday with winds and seas remaining calm through the start of next week. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR/SHORT TERM...Cannon Long Term...Curtis
Area Forecast Discussion
National Weather Service Reno NV
146 PM PDT Wed Sep 22 2021 .SYNOPSIS... A slight cooling trend starts overnight into tomorrow with daytime highs hovering just below seasonal averages. Temperatures rebound slightly by Friday and continue with slightly above average values through the weekend. Areas of haze and smoke should be fairly transient as winds diminish this evening before turning mostly to the north and east Thursday morning through Friday. && .DISCUSSION... The main weather highlights this first day of Fall through this weekend will be an increasing easterly low and mid-level flow and reduction in smoke and haze across most areas of the eastern Sierra and far western NV. Slightly cooler temperatures tomorrow but rebounding going into the weekend. High pressure will nose east into the Sierra and western NV this evening into tomorrow as a weak cold frontal boundary exits east into the Rockies. The resulting west-east orientated upper ridge axis will push over across central OR into southern ID. This will result in a mostly northeasterly flow sitting up across western NV and the Sierra that continues into northern and central CA. As this flow pattern continues into Friday, smoke and haze from regional fires will decrease sharply and be directed mostly east of the Sierra Crest. Hi-Res HRRR simulations complement this forecast outcome for the near-term forecast into Friday. By this weekend, the ridge axis will gradually weaken and sag south thus allowing a more westerly mid and upper flow to increase across the region. The resulting upper height falls will steepen thermal gradients across western NV Basins that translate to a return of the typical afternoon zephyr breezes with gusts to 25 mph over the eastern Sierra and far western NV. Unfortunately periods of haze and smoke will once again begin to filter east of the Sierra crest into western NV. But this is all contingent upon regional fire activity. As the upper ridge recedes westward, warm and dry conditions will continue influence the region through this forecast period. Highs tomorrow will be cooler and only rise into the 70s to lower 80s for valleys as cooler air spreads south and southeast over the region in an increasing easterly wind regime. Highs on Friday will rebound several degrees into mostly 80s across western NV valleys with higher Sierra valleys edging up into the upper 70s. EXTENDED OUTLOOK through the middle of next week... * CHANGES: Another cooling trend for next Tuesday-Wednesday with possible precipitation over northern portions of CA/NV. Ensemble cluster and extended model guidance are beginning to show a pattern change by mid-week next week. Any precipitation that results from this anticipated pattern change will be mostly light and confined to the northern Sierra. But it is worth noting that the second week of the autumn season has a long-wave trough pattern digging south across the West Coast before surging bursts of short wave energy into the region. The only nexus will be a split trough pattern separating upper dynamics and moisture into a cooler more dynamic northern branch and a much drier southern extension into the Sierra and Northern NV. Therefore, it is safe to say that forecast confidence is split between a higher much cooler outcome that is accompanied by a drier, more uncertain rainfall prediction over the forecast region. The best bet lies in the increasing probability of gusty conditions Monday-Tuesday as both European and GEFS ensemble guidance show tightening gradients as the upper trough deepens over the western US. One thing is for sure, the upcoming pattern change could reflect in today`s season change. -Amanda && .AVIATION... For today, gusty southwest winds to 20-25 kts, locally to 30 kts, are likely in the afternoon and evening mainly north of US-50. Light to moderate turbulence is expected to increase along and east of the northern Sierra crest due to the increased airflow. Increasing winds this afternoon should mix out most smoke affecting area terminals. Winds turn to easterly Thursday for a shift of any turbulence to over and west of the Sierra Crest. Lighter winds and dry conditions expected through the weekend, until the next low pressure system moves into the region Monday with increasing winds and chances for showers. -Hoon && .FIRE WEATHER... * Breezy winds today may lead to localized areas of critical fire weather conditions. Breezy winds remain on track as a system passes to our north today. Expect gusts in the 25-35 mph range during the afternoon and evening hours. In the higher elevations of the Sierra and northeast California, peak ridge level winds may touch 45 mph. The combination of the wind with dry conditions may produce localized areas of critical fire weather conditions especially the Sierra Front for a couple hours. After today, winds switch out of the north and east. Winds will be lighter for most areas, but some areas over the Sierra Crest along the western slopes will become breezy early Thursday morning and again Thursday night into Friday morning. -Hoon && .REV Watches/Warnings/Advisories... NV...None. CA...None. && $$ For more information from the National Weather Service visit...