Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/08/20

Area Forecast Discussion
National Weather Service Des Moines IA
641 PM CDT Thu May 7 2020 ...Updated 00z Aviation... .DISCUSSION.../Tonight through Thursday/ Issued at 254 PM CDT Thu May 7 2020 Light rain to continue to spread east late this afternoon into the evening hours and mainly to impact the central to southern sections of the forecast area. The high pressure to the north over Minnesota and Wisconsin is showing signs of winning over the rain developing with some decent dry air advecting in from the north. Very high-based showers across western Iowa and much of the rain is having a tough time reaching the surface because of this dry air entrainment. Cut back considerably on pops across the north and east through this evening and even went completely dry for locations near the MN border. Delayed the onset as well, generally east of Interstate 35 as latest HRRR and RAP don`t have rain at OTM until around 00z and still think that is a bit too soon for that location. Lowered QPF amounts as well with the significant amount of dry air to contend against. CAA develops late tonight into early Friday morning and should be a fairly brisk day Friday as mixing increases close to midday. Winds atop the mixed layer range near 30 knots from the northwest, so with plenty of sunshine, certainly believe several locations could have these wind gusts. Thus, Friday will be a brisk day across Iowa and not ideal for early May. Canadian surface high pressure still progged to build into the region and provide a nice radiation cooling setup by Saturday morning. Continued with mention of frost and no changes to ongoing Freeze Watch. With minimum temperatures just barely getting below 32 by Saturday morning, the main impact will be to weak vegetation. Even so, it is entirely likely that the growing season hasn`t really taken off across the northeast. Saturday night into Sunday...another weak shortwave to ride the northwest flow aloft during this time and bring rain and thunderstorm chances to the state. Severe threat is next to NIL and even the chance of just thunder is very low due to minimal instability and moisture as well as weak forcing available. Another cool down anticipated Sunday night into Monday with more freezing temperatures and frost possible across the forecast area. Monday through Thursday...the weather pattern begins to show signs of changing to more spring-like as zonal flow sets up by Tuesday. An upper level trough tries to develop over the west while an area of surface low pressure looks to form by Wednesday into Thursday over the Central Plains. The Gulf of Mexico appears to open up the moisture flow and Iowa looks to be in the vicinity of a frontal boundary during the aforementioned time. Although there remains plenty of discrepancies with timing and location of any system past Tuesday, certainly able to say the thunderstorm chances and thus the severe weather threat will increase across the state by next Wednesday. && .AVIATION.../For the 00Z TAFS through 00Z Friday evening/ Issued at 638 PM CDT Thu May 7 2020 Rain showers are moving from Nebraska into Iowa early this evening. These showers will continue to move east-southeast across most of the state. MCW and ALO may miss out on rain chances due to air being dry near the surface. Overall, conditions expected to remain mostly at VFR. A brief period of MVFR may be possible, especially at DSM and OTM. Overall impacts from these rain showers are expected to be low. Behind the showers, pressure gradient force develops which will lead to gusty winds on Friday. && .DMX WATCHES/WARNINGS/ADVISORIES... Freeze Watch from late Friday night through Saturday morning for IAZ004>007-015>017-024>028-036>039-048>050-062. && $$ DISCUSSION...Podrazik AVIATION...Krull
Area Forecast Discussion
National Weather Service Marquette MI
624 PM EDT Thu May 7 2020 .SHORT TERM...(This evening through Friday) Issued at 421 PM EDT THU MAY 7 2020 WV imagery and RAP analysis indicated an amplified pattern with a mid/upper level ridge through western North America and troughing over the east. A mid level low was located over northern Ontario with several embedded shortwaves on its perimeter. One shrtwv was sliding east of Lake Superior while another stronger upstream shrtwv was diving south southeast toward the northern Great Lakes. At the surface, high pressure over northern Manitoba extended into the Northern Plains. A weak sfc trough was moving through northern Lake Superior. Tonight into Friday, as the trough moves through Upper Michigan this evening, some sct -shsn are expected to develop. Later tonight as the upstream shrtwv and associated cold front with a batch of even colder air will move in tonight snow showers will increase with some accumulations expected. 850/700 mb temps dropping to around -14C/-25C in the deeper cold air and moisture will support lake effect/enhanced convection for some heavier snow showers toward daybreak and into the morning hours. Accumulations of an inch or two will be possible over mainly north central Upper Michigan, especially over the higher terrain. As high pressure build into the area into the afternoon with lowering inversion heights and more anticyclonic low level flow, any remaining -shsn will diminish. Otherwise, look for high temps well below average with may locations likely to see record low highs. Gusty north winds to 15 to 25 mph will also make it feel colder. Although min RH values will also fall to near 25 percent over the south, the colder air may help to reduce fire weather concerns. .LONG TERM...(Friday night through Thursday) Issued at 409 PM EDT THU MAY 7 2020 The well-below normal temps continue Friday night. After bottoming out in the afternoon, 850 mb temps actually rise slightly through the night from around -11 C at 00z to about -9 C by Saturday morning. Still plenty cold though, especially for this time of year. A secondary mid-level vort lobe will reinforce the cold and help generate enough additional lift that combined with the lake surface- 850 mb delta T`s around 13-15 C there will be another round of light lake-effect snow showers. These will be confined to the NNW wind LES belts of the east downwind of the long axis of the lake. This round of LES looks overall less robust than tonight`s and only another half inch or so of snowfall is expected from eastern Marquette County through Alger and Luce counties. One thing to note is that some model blends didn`t seem to be capturing how cloudy it will (probably) be Friday night with all the lake moisture around. Had to significantly increase sky cover in this forecast over the NBM initialization for the Friday night period. That cloud cover starts to clear somewhat on Saturday which in turn helps temps start to climb out of the ice box - but not a lot, especially over the east where lake-effect clouds persist even though after PBL becomes too dry to support continued snow showers. Highs likely won`t get out of the 30s or much above 40 out there on Saturday. In the sunny areas, mixing to about 1500 m under the strong May sun should support highs in the 40s - better than tomorrow but still well below normal for this time of year. The deeper mixing will also allow RH values to fall to as low as 20% in the sunnier west, but thankfully these temps will mostly be too cold to support fire growth. Sunday`s fast-moving Saskatchewan Screamer still looks to miss us to the south; if anything, models today have trended even farther south with it. Only the CMC brings measurable precip as far north as our side of the Wisconsin line but given the continued support among the GEFS of the drier/more suppressed deterministic GFS solution, have kept things dry for Sunday across the CWA. The next shot of colder air moves in Sunday night and peaks Monday morning. The NAEFS and EC ens once again show 850 mb temps approaching the baseline for the coldest temps in their respective climatologies. This go around the parent short wave is much less impressive and the air aloft is drier, which means despite the chill it will at least be sunny on Monday. That also means deeper mixing and surface temps that can still climb somewhat beneath the strong May sun even despite these very cold temps aloft. Mixing to at least 1500 m again will support highs in the upper 30s to mid 40s which, though not as bad as tomorrow, is still close to record cold highs in Marquette and perhaps a few other areas. The very dry air aloft behind this dry cold front could allow RH to fall below 20%, especially over the west, but once again the cold temps will limit fire weather potential and there will also be less wind with this cold shot too which is even better. The overall dry pattern continues through the middle of next week though models show we thankfully break out of this eastern U.S. ridging pattern and temps finally climb to within a few degrees of normal for mid May. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 624 PM EDT THU MAY 7 2020 Gusty north to northwest winds will prevail with gusts to 20 to 25 knots. Snow showers will move in tonight as colder air move in. Confidence is low whether vsby will signficantly affect. However, cigs are likely to drop to MVFR by Fri morning at KSAW where upslope flow is greatest. Otherwise, cigs are likely to remain VFR at KIWD and KCMX. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 421 PM EDT THU MAY 7 2020 Winds will increase tonight as another batch of colder air moves over the lake bringing winds into the 20-30 knot range. While 20- 30kt nnw winds will continue Fri across the east half of the lake, winds will fall back to mostly under 20kt over the west half. Conditions on slowly improve to about 25 knots across the east half with winds blo 20 across the west. Periods of winds of at least 15- 25kt will linger into Sun and Mon, particularly over the e half of Lake Superior before relaxing blo 20 knots by Tuesday. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...JLB LONG TERM...RJC AVIATION...07 MARINE...JLB
Area Forecast Discussion
National Weather Service Nashville TN
735 PM CDT Thu May 7 2020 .UPDATE... FOR EVENING DISCUSSION. && .DISCUSSION... A surface ridge has slipped east of Middle Tennessee, and mid and high clouds are increasing from the west. The evening sounding from OHX shows a dry column still in place, with PWAT a puny 0.42" and a warm nose centered around 700 mb. A frontal system is coming together to our west and will move quickly eastward. The HRRR shows light showers developing in Middle Tennessee after 06Z, although the low levels are so dry that it will take time for rain rates to increase and cloud ceilings to build downward. Showers should become a little heavier after 12Z once the atmosphere becomes more saturated. Hourly forecast grids are holding up well thus far, so no forecast changes are planned at this time. Will update the public forecast later this evening for wording changes only. && .AVIATION... 00Z TAF DISCUSSION. BNA/MQY/CKV/CSV...A surface ridge is sliding across Middle Tennessee this afternoon, and this will set up some return flow just in time for the next low pressure system. A low center currently situated over the TX panhandle will race eastward overnight and bring a frontal system through Middle Tennessee tomorrow. Look for showers to begin spreading into the mid state before 12Z, with rainfall rates increasing during the morning as ceilings lower to MVFR. Also look for surface winds to increase considerably as the low bisects the mid state. Winds will shift to the NW during the afternoon as the showers taper off. && .OHX WATCHES/WARNINGS/ADVISORIES... Freeze Watch from late Friday night through Saturday morning for Bedford-Cannon-Clay-Coffee-Cumberland-De Kalb-Fentress-Grundy- Jackson-Macon-Marshall-Overton-Pickett-Putnam-Robertson- Rutherford-Smith-Sumner-Trousdale-Van Buren-Warren-White-Wilson. && $$ DISCUSSION......08 AVIATION........08