Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/17/20

Area Forecast Discussion
National Weather Service Denver/Boulder CO
939 PM MDT Sun Aug 16 2020 .UPDATE... Issued at 934 PM MDT Sun Aug 16 2020 Forecast is on track with no significant changes needed. LIght easterly winds have pushed across the Continental Divide and are bringing a bit more humidity to the fire areas, as well as pushing most of the smoke more to the south and west, though there`s still a plume over the Front Range foothills from the Cameron Peak fire. In general, fire activity the next couple of days should be dominated by upslope/downslope wind regimes with afternoon plumes drifting mostly south and west but with less definition/more dispersion than in previous days. && .SHORT TERM...(This evening through Monday) Issued at 335 PM MDT Sun Aug 16 2020 Current satellite and radar imagery shows isolated to scattered convection over the eastern plains where better low level moisture resides. MLCAPE is near 1000-2000 J/kg, but 0-6km bulk shear and effective shear is rather weak (<25 knots) so looks like we`ll just see a couple pulse strong/low end severe storms. Smoke due to the existing wildfires continues to plague the area. The highest concentration per the HRRR shifts the bulk of the smoke across the mountains and high valleys tonight as the mid level flow shifts southeasterly. That should help some of the I-25 Corridor, but hard to say how much of this smoke can scour/mix out this afternoon and evening before inversions settle back in. High mountain valleys will likely see the worst of it through Monday morning. Monday will feature a continuation of above normal temperatures and mainly dry conditions. There is at least a little push of moisture across the mountains and high valleys with the southeast mid level flow tonight, but most of that will mix out tomorrow. That said, we see a narrow corridor of isolated to scattered showers and thunderstorms developing from Park County across the Front Range mountains and foothills. An isolated storm or two could drift off the Palmer Divide or Cheyenne Ridge late in the day, but overall most convection will be tied to the higher terrain. .LONG TERM...(Monday night through Sunday) Issued at 335 PM MDT Sun Aug 16 2020 It looks like a long week ahead for those who are involved in the wildfire suppression industry. The medium and long range models show no appreciable change in the upper air pattern over the western United States through next Monday. The strong upper level ridge centered over Utah today is forecast to be in the same position come next Monday morning. This will hold the very warm airmass in place over the state, generating afternoon high temperatures well above normal through the week. On the plains, this means more 90 degree readings each day. The one thing that will be subtly changing through the week is the amount of moisture rotating under the ridge. The GFS and ECMWF hint at some afternoon shower development over the mountains each afternoon of the forecast period. This will depend on how much moisture is able to either move anti-cyclonically over the ridge and move in from the north, or come into eastern Colorado from the southern plains. There has been some thunderstorm activity over the far eastern Colorado plains over the last couple days, so it is possible that some of this moisture could make it back to central Colorado by Tuesday afternoon. In either case, the chance of thunderstorms over the mountains comes back into the forecast Monday afternoon and continues through the week. These storms will be more likely to be high-based with gusty winds and dry lightning than producers of wetting rains. This will produce the less than desirable situation where additional fire starts are going to be possible, because the last few days have shown how dry and ready to burn the mountain fuels are. On the plus side, pressure gradients across the state will not be that strong, so winds should generally be light to moderate, following diurnal upslope and downslope patterns. The generally dry and stable airmass should also allow for favorable flying conditions, allowing air support to fire operations to continue. && .AVIATION...(For the 06Z TAFS through 06Z Monday night) Issued at 934 PM MDT Sun Aug 16 2020 VFR through Monday. There will be some smoke in the Denver area, and especially over the mountains. There should be less over Denver on Monday, but it could impact slant visibility over the mountains. There`s some uncertainty about whether winds will rotate through northwest Monday morning or just go light and then pick up from the east or northeast around midday. Speeds should be under 8 knots either way. && .FIRE WEATHER... Issued at 335 PM MDT Sun Aug 16 2020 Only moderate humidity recovery is expected in the existing high country fires tonight. Fortunately winds will remain light. The lighter winds will prevail through Monday with an upper level ridge dominating our weather pattern. However, above normal temperatures and extremely dry fuel conditions remain. There is just a slight increase in humidity levels, but even then minimum RH drops to 10-15% over most areas west of the Front Range. The eastern slopes and plains will see a little higher humidity readings closer to 14-22% for mins. The next potential problem we`ll start to deal with as early as tomorrow will be dry lightning. There is just enough moisture to produce isolated storm coverage, but only light if any rainfall. Most of these storms will be along the spine of the Front Range and points east into the foothills, as it`s simply too dry farther west to support convection. Tuesday will continue with elevated fire danger and still very low humidities expected in the afternoon with just a slight chance for a late day shower or storm. Moisture levels will increase during the week with a better chance for showers and thunderstorms. But low level humidity levels will still drop in the afternoons, and overnight recoveries will be modest. Any thunderstorm activity will probably not be able to generate appreciable amounts of precipitation, so the threat of dry thunderstorm activity and additional fire starts will continue much of the week. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Gimmestad SHORT TERM...Barjenbruch LONG TERM...Dankers AVIATION...Gimmestad FIRE WEATHER...Barjenbruch
Area Forecast Discussion
National Weather Service Des Moines IA
655 PM CDT Sun Aug 16 2020 ...Updated Aviation Discussion... .SHORT TERM.../Tonight through Monday Night/ Issued at 236 PM CDT Sun Aug 16 2020 Confidence: Medium to High Currently have a thin band of showers and perhaps iso thunder over the northeast/northwest areas of Iowa. Just southwest of there, the HRRR is focusing more initiation over northeast Nebraska by 20 to 21z. This is expected to expand and drift south southeast into the evening hours. We continue in a marginal risk over the far northwest counties to about Denison with perhaps a small risk of a wind gust this evening. The H850 trough and warm air advection causing the convection will shift south of the region later this evening while another weak "backdoor" boundary drops south southwest into northeast Iowa and then heads south overnight. This will result in cooler temperatures over the north/northeast while the far south continues milder overnight. Lows tonight will drop to the upper 50s to 60 north and in the lower to mid 60s in the south. Some clouds will linger into early Monday morning before high pressure over Minnesota drops south into southern Minnesota by 00z Tuesday. With cooling trends aloft across the north, H850 temps will fall to around 11-12C over the northeast to the mid teens southwest with some stratocumulus behind the boundary. Highs Monday will be about 5 degrees cooler than today with the clouds and southward advection of cooler air. .LONG TERM.../Tuesday through Sunday/ Issued at 236 PM CDT Sun Aug 16 2020 Confidence: Medium From Tuesday onward, a similar patter will repeat. High pressure will pass south of the area with return flow and warm air advection Tues night and Wednesday. With west southwest flow beginning to persist for much of the week, temps will be on the increase to seasonal or slightly above normal for Wednesday through Friday with highs in the lower 80s north to the mid to upper 80s south. Lows will generally be in the 50s to 60s. Toward Friday into Saturday a stronger short wave will drop south across the region and pull a cold front into Iowa. Ahead of this more organized system, the chances for stronger storms will increase by Friday into Saturday. There remains some uncertainty on timing with the GFS about 12 to 18 hours faster than the Euro, though the shear instability parameter space for both models suggests some potential of severe weather. With the slower Euro solution, warmer temperatures are likely to hold on longer into the weekend. && .AVIATION.../For the 00Z TAFS through 00Z Monday evening/ Issued at 652 PM CDT Sun Aug 16 2020 VFR conditions to prevail throughout the TAF period. Might see a stray storm at FOD and DSM this evening, but left out mention attm as currently radar trends and latest hires model runs keep anything that develops west. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...REV LONG TERM...REV AVIATION...Podrazik
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1150 PM EDT Sun Aug 16 2020 .AVIATION... Prevailing VFR conditions throughout the taf period. Pocket of mid level moisture will lift across central lower MI this morning, leading to some increase in higher based cloud cover accompanied by perhaps a few showers...mainly at MBS/FNT. A steady increase in high based diurnal cu then expected throughout Monday under standard diurnal destabilization. Sufficient instability will exist to support a few widely scattered showers and thunderstorms mid afternoon through early evening. The limited coverage precludes a defined mention at this stage. For DTW...Isolated thunderstorms possible Monday afternoon /18z- 22z/. .DTW THRESHOLD PROBABILITIES... * Low for cigs briefly at or below 5000 ft late morning/early afternoon Monday. * Low for thunderstorms impacting the terminal Monday afternoon. && .PREV DISCUSSION... Issued at 311 PM EDT Sun Aug 16 2020 DISCUSSION... The mid level wave responsible for this mornings convection will depart east of the forecast area over the next couple of hours. This will allow for the mid level subsidence bubble in its wake (now affecting most of central and western Lower Mi) to expand across the rest of Se Mi by early evening, ending the risk of additional showers. A seasonally strong upper jet max (100-110 knots) will dive down into the wrn Great Lakes by Mon morning, within the base of the amplifying long wave trough over nrn Ontario. There is some degree of support from the NAM and HRRR in showing a region of mid level moisture pushing into Se Mi late tonight/early Mon morning within the lead edge of this upper jet max. Mid level lapse rates within the moist plume suggest some isolated high based showers are possible late. Mid level height falls will overspread much of Se Mi and Lake Huron on Monday as the upper trough continues to amplify as it dives toward the ern Great Lakes. This will also force another surface cold front into Se Mi. Although limited, model soundings suggest there will be enough moisture for diurnal heating to initiate some convection, isolated to scattered at best. While most of this should be shallow, model soundings indicate at least some opportunity for deep convection late Mon afternoon, especially given steepening 850 to 500mb lapse rates. Diurnal mixing will be supportive of highs in the upper 70s to low 80s Monday. The passage of the cold front will drive even cooler air into Se Mi, with 850mb temps now forecast to drop to +8 to +9 C over Se Mi by Tuesday morning. Mid level confluence will take hold across the Great Lakes on Tuesday as the upper trough rotates across ern Canada. This will support an expansive region of high pressure building into the area from the west Tues and Tues night. Some moisture flux off Lake Huron on Tues will support a fair amount of diurnal cu. This and the cool airmass overhead will suppress daytime highs to the 70s. Recent trends in the medium range model suite maintain some degree of sfc high pressure/low level anticyclonic flow across the southern lakes through the end of the week, supporting a dry forecast. A gradual rebound in the heights and return flow around the sfc high will lead to a modest warming trend Thurs into the beginning of the weekend. MARINE... The cold front responsible for morning showers and storms has nearly exited into Canada. Expect the front to fully clear by 20Z as the final clusters of showers drift east over far southern Lake Huron and western Lake Erie. Conditions are becoming unfavorable for waterspout development, and winds will diminish to around 10 knots overnight with the exception being northern Lake Huron. Daytime showers and thunderstorms are possible with a secondary cold front on Monday, although coverage will be sparse. Increased wave action arrives Monday night given a more constricted surface gradient. A Small Craft Advisory will probably be needed as max wave heights exceed 5 feet from Port Austin to Port Sanilac catching the stronger NW fetch with shore-parallel flow. Winds begin to weaken mid-morning on Tuesday with mainly dry conditions expected through Thursday as Corn Belt high pressure expands into the central Great Lakes. Model consensus regarding the development of a low pressure system through The Straits on Wednesday remains low. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....MR DISCUSSION...SC MARINE.......KK You can obtain your latest National Weather Service forecasts online at
National Weather Service Hastings NE
631 PM CDT Sun Aug 16 2020 ...AVIATION UPDATE... .SHORT TERM...(This evening through Monday) Issued at 237 PM CDT Sun Aug 16 2020 Another frustrating and humbling 24 hrs ahead, with more finicky storm chances and poor model performance. The set up... There is a minor midlevel short wave with an associated sfc cold front draped across our north. Currently we are looking at a very similar set up to Friday. Convection has already started to fire up along the front to our west and to our northeast. This is a bit concerning already that we might see a split across our CWA where we end up getting the shaft. Models certainly haven`t had a good handle on this, and still don`t. The hi-res models and the GFS are rather splotchy, and the 18Z HRRR does have it splitting around us. As far as timing goes, best chances of seeing severe weather is between now and 10pm. Tricky, trigger-happy events like this are to be expected during the summer time under a northwest flow regime like this...but that doesn`t make it any less frustrating to forecast. Regarding severe potential... There is a severe thunderstorm watch in effect from now through 9pm tonight. With favorable sfc and midlevel lapse rates, roughly 3k-4k J/kg of CAPE, and 30-40 kts of shear, at least several strong if not a few severe thunderstorms are possible. SPC has most of the area in a slight risk except for the far southeast since storms are expected to weaken and die off more by the time the front gets there. Severe threats are expected to be up to tennis ball size hail and damaging wind gusts to around 70mph. Now for the rest of the particulars for today and tomorrow... I did bump highs up a bit today given our recent trend of being just slightly under done the last several days...though I was a bit hesitant to do so, given the storm potential. Also brought dewpoints up by a few degrees as well. For lows tonight, I kept fairly close to the previous forecast, if not slightly warmer due to the potential for heat loss to be mitigated by any storm cloud cover. Tomorrow begins the start of a much quieter period with more northerly flow aloft and northerly flow at the sfc. Expecting modestly warm highs generally in the 80s and touching 90 in just a few spots. .LONG TERM...(Monday night through Sunday) Issued at 237 PM CDT Sun Aug 16 2020 Admittedly since most of the time was spent working on the short term, not a lot of focus was placed on the longer term. So keeping things fairly generalized... We look to be getting into a blocking pattern aloft where we are sandwiched between an amplified ridge over the western CONUS and a modest trof over the eastern CONUS. This will keep us in a northerly flow regime aloft, and will also keep most of the week dry. The only precip chances over the remainder of the 7-day period are on Tuesday night and Thursday night. Tuesday is likely the result of another minor midlevel short wave, and the PoPs right now are below "likely" and will probably stay that way, but at least this has been consistently in the forecast over the last few days. Wednesday and Thursday look like they could be the warmest days of the week, though not by much, with highs right around 90 across the board. Thursday looks like repeat of Tuesday, again with PoPs below "likely". && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday) Issued at 629 PM CDT Sun Aug 16 2020 The main focus is obviously the ongoing storms across the area. Main impacts we`re seeing right now are large hail, damaging wind gusts, and heavy rain reducing visibilities to less than a mile. Once this front finally makes it through things are expected to clear up rapidly on the back side. This is clearly evident on satellite currently where the front is rather obvious with clear skies all across western and northern NE. && .GID WATCHES/WARNINGS/ADVISORIES... NE...NONE. KS...NONE. && $$ SHORT TERM...Shawkey LONG TERM...Shawkey AVIATION...Shawkey
Area Forecast Discussion
National Weather Service Grand Junction CO
628 PM MDT Sun Aug 16 2020 .SHORT TERM...(Tonight through Monday night) Issued at 250 PM MDT Sun Aug 16 2020 Another dry day across the Western Slope with precipitable water values only running 43 percent of the climatological normal for mid August. The persistent area of high pressure is currently centered just to our west with moisture riding around the periphery of the high evident on satellite this afternoon. This includes the far Southwest San Juan Mountains with just enough moisture brushing the area and producing weak returns on radar. No evidence of any rainfall reaching the ground with this activity so gusty outflow winds will remain the primary threat through the evening hours before showers diminish around sunset. Elsewhere, the two major wildfires burning in our forecast area...Pine Gulch and Grizzly Creek...continue to run hot with 90 to 100 degrees C fire temperature estimated by satellite. Smoke from these fires has been and will continue to plague the surrounding lower valleys with the latest HRRR Smoke extending the poor air quality further towards southeast Utah and southwest Colorado. Visibilities will likely be reduced overnight as the smoke becomes trapped underneath the inversions. Enhanced drainage may briefly enhance winds in the Grand Valley and Glenwood Canyon, but overall the high pressure should keep winds on the light side. The smoke has also kept high temperatures slightly cooler than guidance and this trend will continue on Monday. Regardless, temperatures are still running above normal with triple digit heat possible across portions of east-central and southeast Utah as well as west-central Colorado on Monday. Monday will also see the high reposition slightly, allowing for a gradual increase in moisture. This will be most evident across southwest Colorado with PWATs increasing to around 0.60 to 0.70 inches Monday afternoon. Isolated to scattered showers and storms will develop but again, the dry low levels evident in Bufkit soundings will keep the potential for wetting rains low. The northern tier of the forecast area will see critically low humidities with dewpoints only projected to climb into the mid 20s to low 30s. Smoke will again be an issue as the upper level flow remains the same, particularly into the overnight hours. .LONG TERM...(Tuesday through Sunday) Issued at 250 PM MDT Sun Aug 16 2020 Little significant change indicated in the pattern during the extended period. The high will wobble from the southern Great Basin to the Southwest then back late in the period. As aptly pointed out in the previous discussion, mid-level heights reach their peak on Tuesday and the highest temperatures during the period are expected to be reached then. Temperature forecasts present a challenge for areas where smoke is most dense as this has limited highs for some areas over the past several days. Regardless, afternoon temperatures will continue to run well above normal, though overnight lows will continue to be relatively cool. In terms of sensible weather, moisture gradually works inward over the area from the periphery of the high which leads to an uptick in shower and thunderstorm coverage from Thursday through Monday. This activity will incrementally increase moisture in the sub-cloud layer leading to a better potential for wetting rains. Meanwhile, a slow rise in dewpoint levels combined with rainfall should begin to mellow fire behavior on the Pine Gulch and Grizzly Creek fires. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 551 PM MDT Sun Aug 16 2020 MVFR visibility is possible over the next 24 hours as smoke from the wildfires settle into the Eagle and Colorado River drainages. A smoke layer will be around as well but for the most part skies will be clear to mostly clear. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...MMS LONG TERM...NL AVIATION...TGJT
Area Forecast Discussion
National Weather Service Green Bay WI
638 PM CDT Sun Aug 16 2020 Updated aviation portion for 00Z TAF issuance .SHORT TERM...Tonight and Monday Issued at 237 PM CDT Sun Aug 16 2020 The latest RAP analysis and satellite/radar imagery show shortwave energy moving across western Lake Superior early this afternoon. Cumulus started to pop in the 10-11 am hour over the Upper Peninsula and northern WI, and mesoanalysis shows that temps are closing in on their convective temps over much of the area. Surface-based instability is rising above 1000 j/kg over northern WI where the high resolution models are indicating scattered showers and storms developing during the rest of the afternoon. With that sort of instability, dry mid-level air, and inverted V soundings in the low layers, could see any storms have the ability to produce brief strong, gusty winds. Will leave a mention in the HWO. The area most likely to be impacted remains far northeast WI into the northern Fox Valley and Lakeshore areas. Besides the thunderstorm potential this afternoon, forecast concerns mainly revolve around temps and fog potential. Tonight...A few showers and storms will be ongoing over northeast Wisconsin early in the evening. Intensity will relatively quickly wane as diurnal instability is lost. Skies should then clear at most locations thereafter. The exception will be over central WI where some high res models show a few showers approaching central WI after midnight in the left front quad of a jet streak. Not confident in the details so will keep the area dry. Otherwise, the jet energy may bring in some clouds at times, but that shouldn`t have much of an impact on temps, which are projected to fall below the cross-over temp at many locations across north- central and central WI. So will add a patchy fog mention late tonight. Lows ranging through the 50s. Monday...High pressure will be gradually building towards the region from the northern Plains. The atmosphere will be more stable tomorrow, partly because of cooler low level temperatures. As a result, should see some convective clouds build with heat of the day, but precip chances are too low to mention. Highs ranging from the lower to upper 70s. .LONG TERM...Monday Night Through Sunday Issued at 237 PM CDT Sun Aug 16 2020 Monday night into Tuesday night: A surface ridge is expected to linger/becoming reinforced across the area through much of Tuesday, allowing for lighter winds and mainly dry conditions. Tuesday night, a nearly east-west oriented cold front is expected to slowly sag south toward the northern part of the area. The main impact for Tuesday night will be increasing cloud cover. Aloft, northwest flow will linger across the area, allowing for somewhat cooler conditions. High temperature will be in the mid to upper 70s for most locations, with a few 80 degree readings south. Overnight lows will drop into the 40s to around 50. Wednesday through Wednesday night: The aforementioned cold front is expected to sag southward into much of northeast Wisconsin late Wednesday afternoon into Wednesday night. This reflects a much slower progression than earlier model run had indicated. This front is currently progged to drop slowly south through all of northeast Wisconsin before departing to the south by late Wednesday night. The front doesn`t have a lot of moisture to work with as the Gulf is continuing to be cut off through much of the first part of the week. The main area of moisture associated with this feature will drift into the area from the northwest, across central Canada. With that in mind, models are showing enough forcing and instability along the front to touch of some showers and thunderstorms through this time period. Only minor rainfall accumulations are being painted out by the models as has been the trend over the past couple days. Lows are expected to be in the 50s with highs warming into the 70s to around 80. Of course, temperatures could be held back a bit if cloud cover is extensive during the day. Thursday into Thursday night: Much of northeast WI is expected to be between systems during this time period, which may give a brief break in the precipitation. This is not a definite as the northwest flow and afternoon heating may destabilize enough to allow for afternoon shower and thunderstorm development. Cloud cover will increase during the afternoon as well. Temperatures are expected to moderate to some extent as the flow deamplifies very slightly. Will still be in northwest flow, but not quite as aggressive. as the upper-level flow flattens across the area. Lows will be mainly in the 50s with highs warming into the upper 70s to low 80s. Rest of the extended: Moisture is expected to increase across the area toward the end of the week into the weekend, allowing for increased chances for showers and thunderstorms. The upper-level pattern may begin to amplify once again during this time period with a stubborn ridge parked across much of the western CONUS. This would allow several disturbances to pass through the area, allowing for a bit more unsettled weather pattern for next weekend. The unsettled weather along with the potentially amplified northwest flow will act to keep temps a bit cooler as well. At this point, temperatures would be near to slightly below normal. No major changes were made from the model consensus. && .AVIATION...for 00Z TAF Issuance Issued at 637 PM CDT Sun Aug 16 2020 Once the scattered showers and isolated thunderstorms dissipate/clear the area this evening, generally good flying conditions are expected for the rest of the TAF period. Diurnal convective clouds will develop again tomorrow, but bases should be VFR. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....MPC LONG TERM......Cooley AVIATION.......Skowronski
Area Forecast Discussion
National Weather Service Grand Rapids MI
1005 PM EDT Sun Aug 16 2020 LATEST UPDATE... Update .SYNOPSIS... Issued at 308 PM EDT Sun Aug 16 2020 - Quiet weather next several days && .UPDATE... Issued at 1005 PM EDT Sun Aug 16 2020 The convective shortwave that helped to cause the thunderstorms over WI has moved over northern Lake Michigan as of 945 pm. The RAP model shows a small area of upper divergence and surface convergence that is supporting this convection. The SPC SREF 3hr calibrated thunderstorm forecast is tracking this area well. It does show it weakening and moving onshore near Hart. What concerns me is we have a 100 knot polar jet core over NE WI now that will be over Lake Michigan by 3 to 4 am. The RAP (and other models) show very strong upper divergence developing over east central Lake Michigan at that point. Also the MU cape on the NAM, SREF, and RAP model jump to near 2500 j/kg near the lake shore. While that is happening a sort of meso-low seems to want to develop near MKG. I have to wonder with all of that going on if we would not get come convection developing. After all the south buoy water temperature was 75 degrees an hour ago. The 5 pm run of the RAP model sounding just off shore of Holland had only 35 CIN and 2400 surface based cape. There was some dry air near 500 mb but it was mostly moist till 500 mb and than moist again to near 250 mb. Since the latest hi- res models do not have much convection, I have 20% pop near the lake shore during the early morning hours just in case something does develop. UPDATE Issued at 640 PM EDT Sun Aug 16 2020 I have updated our forecast (grids) to indicate showers are possible near and west of US-31, north of South Haven from just before midnight till just before sunrise. A thunderstorm would not be out of the question. There currently is a shortwave touching off some showers and thunderstorms over the Michigan Upper Peninsula that is dropping southeast. Both the NAMNEST and RAP model show 2000 to 2500 j/kg of MU cape from mid Lake Michigan to the Lake shore from midnight till sunrise. The instability just gets to US-31. Likely the warm lake and cold air at mid levels is helping the cause for convective instability. The SPC SREF shows a 5 to 10 pct chance of thunderstorms over a same area at the times I indicated above too. The HRRR, HRRR Experimental, HREF, RAP and NAMNEst show convection associated with this making to the lake shore after midnight tonight. I do no think this will be a big deal but it is enough for a 20-30 pct pop near the lake shore after midnight. The bottom line is I have scattered showers near the Lake Michigan shore overnight until around sunrise. && .DISCUSSION...(This evening through next Sunday) Issued at 308 PM EDT Sun Aug 16 2020 - Quiet weather next several days No real impact weather to write about today as the front is through and only a few chances for scattered showers exist next week. The first chance is tonight as shortwave trough axis digs into the central Great Lakes and the large scale western CONUS ridge and eastern CONUS trough pattern amplifies. Only light showers expected across the northern zones. Steepening lapse rates on Monday along with sufficient mid level moisture will bring diurnal enhancement of cu and low chance of showers away from Lake Michigan on Monday, Another shortwave trough and surface cold front advances into Lower Michigan on Wednesday with a low chance of showers. We expect most places will remain dry this entire week and with the low humidity and comfortable temperatures, it will be a perfect week for outdoor activities. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 640 PM EDT Sun Aug 16 2020 I expect VFR conditions to rule our TAF sites for tonight through Monday into Tuesday (and beyond). However there are 2 glitches. The first glitch is a shortwave dropping southeast from western Upper Michigan this evening. It may bring a few showers to the MKG and GRR taf sites in the 06z to 09z time frame. I put VCSH to cover this possibility. It would not be out of the question there would even be an isolated thunderstorm but that chance is fairly low. The next glitch is the strongly digging northern stream jet core is aimed at Southwest Michigan on Monday. There will be instability inland Monday afternoon. So do expect scattered showers and thunderstorms inland of US-131 Monday. I put VCSH for our easter TAFS for that event. Winds will be northwest around 10 knots Monday but should be southwest around 5 knots toward midnight as the weak system moves into the area. && .MARINE... Issued at 308 PM EDT Sun Aug 16 2020 We will watch for some wind gusts near 25 knots on Monday and Monday evening otherwise winds and waves should be below advisory criteria for small craft most of this week. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ UPDATE...WDM SYNOPSIS...Ostuno DISCUSSION...Ostuno AVIATION...WDM MARINE...Ostuno
Area Forecast Discussion
National Weather Service Marquette MI
754 PM EDT Sun Aug 16 2020 .SHORT TERM...(This evening through Monday) Issued at 348 PM EDT SUN AUG 16 2020 Diurnal CU field across much of the UP developing this afternoon with iso shra across much of the Upper Great Lakes region. Temperatures have climbed comfortably into the 70s across the cwa as developing lake breezes can be observed in GOES and sfc obs off Superior and Michigan. These lake breeze convergent zones will serve as the focus for anticipated convection heading into this evening. CAMs downplayed the event a bit with this morning`s runs and the HRRR continues to be less than amused at tsra chances. Capped chances at 40% across the central and east this afternoon and changed wx into coverage to mention iso to sct wording. Regardless, will need to monitor the next few hours for convection interacting with any lake breezes. Tonight, a weak cold front is progged to pass over Upper Michigan. Front should remain mostly dry, but some models have been hinting at chances of light precip. Look for lows to fall into the 50s, with some temps near 60 along Superior and into the 40s across the interior. Tomorrow, winds will gust into the teens from the north behind a cold front passing late tonight. A few diurnal showers are possible, but have left any PoP mentions out of the forecast for now. Look for potentially hazardous beach conditions east of Marquette and highs climbing to either side of 70...coolest west and warmest along Lake Michigan. .LONG TERM...(Monday night through Sunday) Issued at 339 PM EDT SUN AUG 16 2020 Expect a generally seasonable stretch of weather for much of the upcoming week. Overall upper pattern will be pretty amplified for August standards with significant heat ridge centered over the desert southwest. 50H height will exceed 600 dam into midweek with ridge axis extending up into western Canada. Downstream upper troughing will exist over eastern North America with northwesterly upper flow prevailing across the Upper Great Lakes at least until late in the work week. looked liked most of the week was going to be dry with the best chance of rain not til Friday. Today`s model trends are a little wetter but by no means a washout. Shortwave energy in northwesterly flow will drop into the Upper Great Lakes on Tuesday and Tuesday evening brings some scattered showers. Weak boundary associated with that shortwave will then hang up over or just south of the area through mid to late week acting as a focus for slight to low chance diurnally driven shras and isolated tsra Wednesday and Thursday. By Friday...shortwave energy moving in off the Pacific will flatten the northern extent of the western U.S. upper ridge. Friday into Friday night still looks like the best chance for the most widespread shra/tsra activity but if anything models are in less agreement on how things will evolve Friday through next weekend. Temperatures will be seasonable...generally in the 70s for highs this week. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 754 PM EDT SUN AUG 16 2020 VFR conditions are expected at KIWD/KCMX/KSAW thru this fcst period. Cold front passing during the night will lead to gusty nw to n winds to around 20kt at KCMX/KSAW on Mon. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 302 PM EDT SUN AUG 16 2020 A cold front is expected to pass over Lake Superior tonight as winds become more northerly, gusting up to 25 knots across the east half and 20 knots across the west through tomorrow. High pressure then traverses over the lake through the rest of the week with lighter winds blo 20 knots prevailing. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...JAW LONG TERM...MZ AVIATION...Rolfson MARINE...JAW
...Updated Aviation Forecast Discussion...

.DISCUSSION... Issued at 211 PM CDT Sun Aug 16 2020 Near term... Scattered strong to severe storms are possible this afternoon/evening along a weak cold front moving south through the area late this afternoon into the evening evening. Some of these will be capable of large hail/damaging wind. Synopsis... The region remains in persistent northwesterly flow aloft with a strong ridge of high pressure to our west and persistent troughing to our east. At the surface, high pressure remains centered over central Missouri with southerly low-level return flow extending across central/western KS and Neb. Within this low- level return flow resides a moist airmass with 850mb dewpoints near 14-15C in central Nebraska contributing to an increase in instability to our west and more specifically, across northeastern Nebraska nearest to the surface front where a narrow axis of 65-70F surface dewpoints have pooled. Tonight... Model solutions continue to show scattered convection developing near the frontal boundary by mid-afternoon and continuing south through eastern Neb/southwestern Iowa in broken clusters along the instability axis with RAP effective bulk shear values of 35-40kts. Storms may be capable of producing large hail and damaging winds but cannot rule out an brief isolated tornado. Convection should be fairly progressive and south of the forecast area by 04-06z tonight. Monday and beyond... Surface high pressure will build overhead Monday with highs forecast in the mid to upper 80s. A weak disturbance moves overhead Tuesday night when we have our next chance of light precipitation. A few other subtle disturbances are forecast to move through northwesterly flow aloft and could spark additional showers/thunderstorms later on Thursday into Friday. Overall temperatures will be in the upper 80s with lows generally in the 60s. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 631 PM CDT Sun Aug 16 2020 Scattered thunderstorms will continue for the first hour of the TAF cycle, otherwise VFR conditions with light and variable winds are expected through Monday. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Kern AVIATION...Kern