Area Forecast Discussion
Issued by NWS Hastings, NE
Issued by NWS Hastings, NE
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777 FXUS63 KGID 210024 AFDGID Area Forecast Discussion National Weather Service Hastings NE 724 PM CDT Mon May 20 2024 ...Aviation Update... .KEY MESSAGES... - BY FAR the main issue is the likelihood for at least a few (if not several?) severe storms this evening and overnight, followed by one final round of strong to potentially severe storms mainly during the first half of Tuesday daytime (particularly 9 AM-1 PM time frame). Large hail, damaging wind the main hazards, but a tornado or two is not out of the question especially if any isolated supercells can get established near/after sunset. - Although not as big of a concern overall compared to severe storm hazards noted above, there is at least "some" concern for rainfall being abundant enough/heavy enough in narrow corridors to promote localized flooding/flash flooding tonight into Tues daytime, and a Flash Flood Watch has been issued for most of our Nebraska coverage area (CWA). Please see separate HYDROLOGY section below for more details. - Once any strong/possible severe storms vacate our CWA to the east late Tues AM-early afternoon, we`ll have a fairly quiet and mostly dry 48+ hours (especially Wed) with little to no severe storm threat. - From especially Thursday night onward, our forecast is again "littered" with various/intermittent chances for rain/thunderstorms, as a very active upper air pattern continues. At least for now, there are no "obvious" severe storm threats during this time (and we are not outlooked by SPC), but early signs do point to at least a marginal severe environment returning already Thurs evening and/or overnight. - Temp-wise: Nothing unusual at all for late-May, with highs on most days between the upper 60s to around 80, and lows on most nights mainly 40s-50s. && .DISCUSSION... Issued at 507 PM CDT Mon May 20 2024 -- 7-DAY FORECAST OVERVIEW/HIGHLIGHTS (heavily focused on these first 24 hours): - CURRENT/RECENT WEATHER SCENE AS OF 430 PM: As expected, the vast majority of our CWA (save for some limited shower activity mainly over Webster County this morning) has remained dry and storm-free today thus far. Under what has become partly to mostly cloudy skies, high temps have or soon will top out in the 74-82 range most areas (coolest north/west and warmest south/east. In the mid-upper levels, the main player(s) tonight will be a series of subtle waves embedded in west-southwesterly flow aloft, downstream from the main wave still out over the Desert Southwest that will track directly overhead the first half of the day Tuesday and take any severe storm/flooding out with it. At the surface, nearly our entire CWA currently resides just north of a developing/somewhat diffuse warm front stretched across northern KS, with breezes most areas currently out of the east-northeast 5-15 MPH. Surface dewpoints are seasonably-moist...mainly low-mid 60s. - THIS EVENING-OVERNIGHT: Most of our CWA should remain storm-free until around 7 PM. However, after that, and especially after 9-10 PM, all bets are off as scattered to numerous/widespread thunderstorms are expected to blossom over mainly our Nebraska CWA (along and north of the warm front) as weak upper forcing arrives from the southwest, and the low level jet (evident at 850 millibars) begins to ramp up. Closely leaning on higher-res models such as HRRR, a series of individual storms (possibly supercellular) along with clusters and perhaps broken, mainly west east oriented lines of convection will traverse our area overnight, with a sharp south edge likely somewhere between Highway 6 and the KS border (very little activity expected in KS). The later storms form, there is some question as to how truly surface- based they might be, but at the very least the environment is primed for a large hail and/or damaging wind threat, given mixed-layer CAPE at least 1500-2500 J/kg and deep layer shear 40-50 KT. This is a somewhat concerning environment as it is, and if any storms are able to remain at least semi- discrete/supercellular and tap into increasing low-level shear mainly near/after sunset, then at least a brief/transient tornado threat could be on the table as well, not to mention some hydro concerns (see separate section below). - TUESDAY DAYTIME: Following what could be a relative lull in activity around sunrise, the main upper wave and associated surface cold front will cross overhead by late-morning/early afternoon. As this occurs, one final round of more north-south oriented strong to severe storms is expected to cross much of our mainly Nebraska CWA from west to east between 9 AM-1 PM, perhaps offering up more potential for large hail/damaging winds and localized flooding. Once this activity clears, our severe storm and flooding threat should end, as the severe threat focuses farther east of our CWA through the afternoon and evening. Behind the front, it will be very breezy/somewhat windy on Tuesday, with northwest winds sustained 15-25 MPH/gusts 25-35 MPH. High temps will depend on "exact" frontal timing, cloud cover etc. but we are calling for roughly a 15-degree gradient from mid 60s far north/west to upper 70s far southeast. - TUESDAY EVENING-OVERNIGHT: Most areas will likely remain dry, but isolated to scattered showers and maybe a few WEAK storms could affect some counties mainly south of I-80 into KS through the night. Winds will die down, and this will be one of the cooler nights coming up with lows mainly 44-51 most places. - WED DAYTIME-THURS DAYTIME: This is mainly a DRY/storm-free period in between upper disturbances. High temps low-mid 70s Wed and upper 70s-low 80s Thurs as south winds increase. - THURS NIGHT-SATURDAY: Intermittent shower/thunderstorm chances return as various upper waves move through again. We`ll have to watch Thursday evening/overnight for MAYBE our next, at least limited severe storm chance. -SUNDAY-MONDAY (Memorial Day): The parade of low-confidence rain chances/PoPs continue as both the ECMWF/GFS bring another disturbance somewhere across the Northern/Central Plains. Although still several days out, at least an early glance suggests instability levels fairly muted by late-May standards and thus a lower severe threat. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 724 PM CDT Mon May 20 2024 - General overview for KGRI/KEAR: This is a very complex period, with at least a few (if not several?) rounds of thunderstorms possible through the first 18 hours (some of which could be severe), along with the likelihood for several hours of MVFR/IFR ceilings (mainly after 04-06Z), and finally an increase in northwest winds with breezy to moderately-windy conditions prevailing much of Tuesday daytime. - Ceiling/visibility/precipitation details: Right out of the gate, scattered thunderstorms are in the general area, and off-and-on thunderstorm activity could easily continue through the majority of these first 18 hours, with the best chance for any possible, multiple-hour break most likely focused between 09-15Z. Some of the storms during the period could be severe, which IF they were to directly impact KGRI/KEAR could be capable of producing hail of at least quarter size/wind gusts to 50+KT. By roughly 18Z, all convection should be vacated east of the area. As for ceiling/visibility trends, obviously visibility be reduced at times during periods of heavier rain. As for ceiling, the most pronounced period of MVFR/IFR is expected to focus 04-06Z through 18Z, with MVFR perhaps hanging on until very late in the period closer to 22-23Z. - Winds: Aside from any direct thunderstorm-related influences (which are actually fairly likely at times and could greatly increase speeds and/or result in erratic directions), the basic expectation is for: 1) winds generally around 8-13KT from the east-northeast this evening...2) gradually switching to more northerly at similar speeds late tonight-early Tues AM...3) picking up out of the northwest Tuesday daytime commonly sustained 16-22KT/gusts 25-32KT. && .HYDROLOGY... Issued at 507 PM CDT Mon May 20 2024 -- Various comments regarding the Flood Watch valid officially valid through 1 PM Tuesday for most of our Nebraska CWA along/north of Highway 6: - This should be considered a "lower to medium confidence" Watch situation, as to be perfectly honest the MAJORITY of the Watch area will probably receive no more than 1-2" of rain and experience little (if any flooding). - However, due to the POTENTIAL for one or two west-east oriented corridors that could see "training" of storms with localized higher amounts perhaps as 3-5", felt it was best to proactively issue a Watch...in coordination with neighboring WFOs to both the west/east. Fortunately, most places have received only around 1" or less of rain in the last week, so our ground is not overly-saturated and should be able to absorb some rain fairly readily. - Please note that the last few HRRR runs (especially since 18Z), have already started to cast a touch of doubt on the placement of this watch, suggesting that the heaviest rain could perhaps target counties mainly between I-80 and the KS border (instead of counties mainly along/north of Highway 6), so the current Watch configuration should not be considered "set in stone". && .GID WATCHES/WARNINGS/ADVISORIES... NE...Flood Watch through Tuesday afternoon for NEZ039>041-046>049- 060>064-072>074. KS...None. && $$ DISCUSSION...Pfannkuch AVIATION...Pfannkuch/Thies HYDROLOGY...Pfannkuch