Area Forecast Discussion
Issued by NWS Hastings, NE
Issued by NWS Hastings, NE
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985 FXUS63 KGID 171053 AFDGID Area Forecast Discussion National Weather Service Hastings NE 553 AM CDT Mon Jun 17 2024 .KEY MESSAGES... - Another day, another VERY UNCERTAIN risk for possible severe thunderstorms mainly in the 5 PM-midnight time frame, as it will be another "battle" between very warm air aloft (serving as a cap) and high instability. IF we end up with a later-day severe threat, it would mainly favor Nebraska areas west of an Alma-Kearney-Fullerton line. - Although hot again this afternoon across most of our area (especially south), heat index readings are expected to be peak SLIGHTLY lower than yesterday, with most of our Nebraska area topping out 95-99 and any possible low-100s most favored in our KS zones (but still short of official Advisory criteria). - This afternoon and especially this evening-overnight will be unusually-windy by mid-June standards, sustained southerly speeds commonly 25-35 MPH/gusts up to around 45 MPH. - A seasonably-strong cold front will arrive Tuesday and stall out near our southern fringes through Wednesday before lifting back north. The net result will be the potential for several rounds of rain/thunderstorms across the region, with not only at least a narrow zone of severe storm potential mainly Tues afternoon-evening, but also a wider swath of perhaps at least 2-4" of rain across much of our area over the course of these 36-48 hours (at least localized flooding possible). - High confidence that Wednesday is the coolest day of the week, with widespread clouds/rain holding most places down in the 60s-70s for highs. - Thursday-Sunday: Although not as overall-rainy as Tues-Wed will be, intermittent, lower-confidence chances for rain/thunderstorms continue almost every day or night for at least parts of our area, with at least occasional/limited chances for strong to severe storms and localized heavy rain. && .DISCUSSION... Issued at 552 AM CDT Mon Jun 17 2024 -- Up front "admin note": Given a very complex short term forecast with multiple pesky concerns/uncertainties, will keep the main part of this discussion focused ONLY on these next 48 hours (through Tues night). -- SHORTER TERM FORECAST OVERVIEW/HIGHLIGHTS (through Tues night): -- CURRENT/RECENT WEATHER SCENE AS OF 5 AM: On a very positive note (and as suspected as a definite possibility here in last few discussions), most of our coverage area (CWA) was "saved" from a severe thunderstorm threat Sun afternoon-evening as a strong cap (warm air aloft) held firm. Although we had one radar-indicated marginally-severe storm in Phelps/Harlan counties, it quickly died with nightfall, and the vast majority of stronger overnight and ongoing activity has concentrated at least slightly north of our CWA within the exit region of a strong 40-50 KT low level jet (evident at 850 millibars). That being said, a fairly expansive outflow boundary has settled considerably farther south into our CWA than expected even 6 hours ago...marked by northerly/easterly winds that have worked southward through roughly the I-80 corridor (this will make especially hour-to-hour temperature/wind forecasting this morning VERY tricky). Precip-wise, a smattering of isolated-scattered, high-based showers/thunderstorms (rooted well above the surface) are affecting parts of mainly our western/northern CWA at this time, with especially the northern activity in/near Nance County being aided by the low level jet lifting air upward over the top of lower-level outflow. None of this activity is particularly intense (nor is it expected to be), but occasional wind gusts into 40-50 MPH have occurred near storms. Temperature-wise, the pesky outflow boundary down to near I-80 has dropped much of our northern CWA unexpectedly far down into the 60s this morning, but unseasonably-warm readings in the 70s counties are present especially Highway 6 southward into KS where southerly breezes still prevail (the jury is still out regarding whether or not Grand Island/Hastings will set new record warm low temps for today...as it all depends on the aforementioned outflow (see separate CLIMATE section below for details). -- TODAY-TONIGHT: Will admit up front that confidence in how today plays out is (if anything) a bit lower than even 12 hours ago, especially in the temperature-wind department this morning, as depending on how slowly/quickly southerly winds become re-established, especially parts of our northern half may not get as hot as expected today (stay tuned for potentially noticeable adjustments to hourly and possibly even daily high temps in later forecasts). But, focusing on the basic expectations by topic: - Isolated to scattered (and most likely non-severe) showers/storms will continue to develop/stream overhead through much of this morning, but should gradually diminish fade away with time as the low level jet weakens. - Other than perhaps some rogue sprinkles/very spotty showers, the vast majority of our CWA is probably looking at a dry afternoon-evening. - However, like yesterday, it will be another battle between warm air aloft (mid level/700 millibar temps even warmer than yesterday...at least 13-15C), and healthy instability/mixed- layer CAPE expected tor each at least 2500-3500 J/kg by peak heating. - Based on how yesterday turned out, feel that UNLESS outflow boundaries from this morning linger around longer than expected and provide a focus for late afternoon-evening storm development, it is quite possible that our ENTIRE CWA will remain capped, with the main potential for severe storms focusing at least slightly off to our west-through-northwest where surface moisture convergence might be a bit more focused. - However, IF anything is able to break through the cap within our northern/western CWA late this afternoon-evening, it could quickly become severe, capable of producing large hail to at least golf ball size, damaging winds 60+ MPH and MAYBE a brief tornado, but this would depend on a mesoscale boundary being present. One limiting factor would be fairly weak deep layer shear of only 20-30KT. Currently expect the post-midnight hours to be dry with activity focusing well to our north by that time. - In summary regarding storm potential: Feel that the SPC Slight/Marginal risk areas are probably plenty generous into our CWA, and should be viewed as very CONDITIONAL (much like yesterday). - Temperature-wise, assuming skies clear sufficiently in time and southerly flow is able to re-establish northward across the CWA, high temps should reach at least the low-mid 90s most areas (upper 90s most favored in KS). Fortunately, heat index values should hold below 100 today most areas (possibly reaching 100 or very slightly higher in KS), but falling short of Advisory criteria. Assuming no "surprise" outflow influences, low temps tonight should hold up in the 70s area- wide. - This afternoon-tonight, deepening low pressure to our west will induce increasing southerly winds area-wide (unusually strong for mid-June). Sustained southerly winds commonly 25-35 MPH/gusts up to around 45 MPH and would not be surprised if a rogue 50+ MPH gust happened overnight especially in our west. - TUESDAY-TUESDAY NIGHT: The main basic story is that a well-anticipated cold front will gradually pass through the CWA from north to south during the day, likely stalling near our far southern/southeast edges by late afternoon. There is some uncertainty into exactly how fast this front moves in, which also leads to resultant uncertainty in temps/location of best storm chances. - Rain/thunderstorm potential: The morning could feature the first spotty, elevated (and likely weak showers/storms) just behind the front. However, by mid-late afternoon (peak heating), a narrow line of strong to severe storms is expected, with higher-res models currently focusing this activity within the southeastern 1/3 of our CWA. This would mainly be a hail/wind/heavy rain threat. Then during the evening-overnight hours, concerns will increase for a POSSIBLE more widespread heavy rain event, as pronounced, west-southwest to east-southeast corridor of convergence develops in the 850-700 millibar layer (north of the surface front). While NOT EVERYBODY will see truly heavy rain, could envision at least a 50-mile corridor of our CWA picking up a widespread 2-4" of rain, and this will need closely monitored for possible flooding concerns (WPC has our entire CWA under a "strongly worded" Slight Risk for excessive rainfall). - Temperatures/winds: Could easily see some areas end up 5+ degrees cooler/warmer depending on exact frontal timing, but for now have daytime highs aimed from low 80s far north/west-central, to mid 80s central, to upper 80s-low 90s far southeast. No matter what, at least slightly cooler than today all areas. Low temps Tues night should bottom out at least 10-15 degrees cooler than Monday night (most areas mid 50s to lower 60). The north winds behind the front Tues daytime do not look overly-strong (gusts probably 20-30 MPH...not as strong as the southerlies out ahead of it). && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 114 AM CDT Mon Jun 17 2024 For KGRI/KEAR Airports: - General overview: Although there are small chances (mainly 10-20%) for a few passing showers/thunderstorms both at some point this morning and perhaps again Monday evening, odds favor an overall-dry period and confidence is overall very high in VFR ceiling/visibility throughout. That leaves moderately-strong southerly surface winds and even stronger low-level winds as by far the main concern (including two separate low level wind shear/LLWS groups). - Ceiling/visibility/rain and thunderstorm potential details: Particularly between 10-17Z, there is a chance that a few showers/likely weak thunderstorms will pass through, but with overall-probability of occurrence and expected impacts fairly low, will only include a generic "vicinity shower" (VCSH) through part of this time frame for now. Although a few to scattered lower-level VFR clouds are possible at times, confidence is overall-high in VFR ceiling/visibility throughout. - Winds: - Surface winds: By mid-June standards, this will be a fairly windy period. Assuming no unexpected influences from convective outflow boundaries, speeds will prevail southerly throughout, with sustained speeds commonly 15-25KT/gusts 25-35KT. - Low level wind shear (LLWS): There are two separate periods of TAF-worthy LLWS during the period, even despite the surface winds being plenty breezy themselves. 1) Right away this morning through around 14Z, southwesterly winds within roughly the lowest 2K ft. AGL will top out around 50KT, promoting roughly 30-35KT of shear magnitude between the surface and this level. 2) This evening (02Z onward), if anything an even stronger southerly low level jet will kick in, with speeds within roughly the lowest 1,500 ft. AGL accelerating to around 55KT, causing fairly strong shear magnitude at least 35-40KT between the surface and this level. && .CLIMATE... Issued at 552 AM CDT Mon Jun 17 2024 -- Regarding possible RECORD WARM LOW TEMPS on Monday (June 17th): Overnight temperatures both this morning (Monday AM) and again Tuesday AM will end up being quite warm, with many places especially south of I-80 holding up well into the 70s. Depending on how far south an outflow boundary manages to drift this morning, potential June 17th records for warmest low temperature COULD be threatened at Grand Island/Hastings airports (the 2 sites for which we issue formal Record Event Reports/RERs). Please note that NO records are expected to be set on Tuesday the 18th, as despite very warm early morning lows, a cold front arriving during the day and evening should easily drop temps safely below record territory by midnight that night. - GRAND ISLAND Record Warm Low Latest Forecast Monday June 17th 74 (1906) 74 (but could abruptly be cooler if outflow boundary passes through) - HASTINGS Record Warm Low Latest Forecast Monday June 17th 72 (2020/2014/1946) 74 NOTE/REMINDER: in order for a new record warm low/minimum temperature to become official it has to "survive" the entire 24-hour calendar day (in other words, it is not always based solely on the early-AM low temp). && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ DISCUSSION...Pfannkuch AVIATION...Pfannkuch CLIMATE...Pfannkuch