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Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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298 FXUS65 KCYS 142330 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 530 PM MDT Sun Jul 14 2024 .KEY MESSAGES... - Red Flag Warning for the majority of southeast Wyoming and portions of the Nebraska Panhandle today. Dry thunderstorms will become scattered to numerous, and possible fire starts from lightning strikes may occur. - Very hot temperatures will continue through Monday. Heat Advisories remain in effect for the High Plains along and east of I-25. - Increased precipitation chances and cooler temperatures are expected late Monday through Wednesday. && .SHORT TERM /THROUGH TUESDAY/... Issued at 145 PM MDT Sun Jul 14 2024 High based thunderstorms beginning to develop across parts of the CWA at 1PM. Seeing lightning strikes across central Laramie County near Cheyenne...and out in Carbon County from Rawlins to Arlington. Beginning to see development across Albany County and southern Platte County as well. Looking at GFS forecast soundings...18Z PWATS range from 0.6 inches out near Rawlins to 0.7 inches in the Panhandle. There is a surface trough analyzed along a line from Pine Bluffs to Casper along the east slopes of the Laramie Range. An upper level vort max moving through the ridge this afternoon providing some upper level lift which will set us up for a pretty significant dry lightning event the remainder of this afternoon into this evening. Looking at HRRR and RAP simulated radar...convection blossoms after 22Z along the Laramie Range with high based storms moving into the Panhandle through 03Z-04Z. Given very dry air in the lower elevations...storms will be high based and mainly dry. Given what we are seeing currently...will keep the Red Flag Warnings going as they are through 10 PM this evening. Local fire customers will need to be on alert for increased fire starts with these dry thunderstorms through mid to late evening. PWATS on the increase for Monday...increasing to an inch across southeast Wyoming and near 1.2 inches in the Panhandle. Better chances for wetting rains. ECMWF/SREF/NAM and GFS all showing fairly widespread QPF across the CWA. Continued high PoPs (50-80 percent) Monday afternoon and evening...that dissipate towards 06Z. These diurnally driven showers and storms will continue Tuesday with good chances for afternoon and evening storms. Long/skinny CAPE profiles suggest storms capable of producing heavy rainfall with these increased PWATS. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Issued at 431 AM MDT Sun Jul 14 2024 For the extended period, weather across SE WY and E NE will be dominated by a persistent ridge of high pressure over the western half of the United States. A broad upper trough centered over Ontario at the beginning of the period will shift east into Quebec by Thursday, allowing the western ridge to expand north and east causing height rises and weakening flow aloft through Saturday. Abundant mid-upper level mositure will continue to round the ridge over WY and W NE. At the surface, persistent southerly/southeasterly flow will keep low-mid-50s dew points in W NE through the weekend. Confidence in the large scale evolution through Saturday is high given ensemble and deterministic model agreement. By Sunday, models begin to diverge on the timing of a trough digging into the northwest US, which may begin to break down the ridge for the end of the weekend and start of next week. For Wednesday, showers and thunderstorms look to be most abundant for this day given the position of the ridge allowing for better flow aloft and embedded disturbances to force development. With PW values ranging from 0.75" to over 1" over much of E WY and W NE, above normal for this time of year, storms that develop could produce heavy rainfall. Flash flooding potential will be enhanced by relatively slow storm movement. Both Instability (adequate moisture beneath steep ll and ml LRs) and borderline deep layer shear (still decent flow aloft) should support a strong-severe storm, especially further east into NE. Temperatures across the region will be the coolest of the forecast, with highs ranging from the low to mid 80s for most. Confidence in the general precip+temp forecast for Wed is moderate-high, with details regarding exact location of storms and severe potential low-moderate. Thursday through Saturday, as the ridge expands and heights rise, flow aloft will weaken, and temperatures will rebound. Although deep layer shear and instability will be slightly weaker, abundant moisture aloft and very deep inverted V profiles will support showers and storms producing gusty winds, along with a dry lightning potential, especially further into WY. The strongest thunderstorm potential will be confined to W NE where ll mositure and shear will be best. High temps each day are expected to rise into the upper 80s to low 90s for the lower elevation areas. Confidence in the forecast during this period is moderate, while that in thunderstorm intensity is low given cross-model and run-run inconsistencies in the degree of ll moisture return and extent during this period. Sunday and beyond, the upper trough digging into the US should dampen the ridge at some point impacting our sensible weather. However, timing and impact differences yield low confidence in when and what that impact will be. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 523 PM MDT Sun Jul 14 2024 West northwest flow aloft will continue, with low and mid level moisture increasing on Monday, producing increasing chances for late day showers and thunderstorms. Wyoming TAFS...Scattered to broken clouds from 8000 to 10000 feet will prevail. Occasional thunderstorms, or thunderstorms in the vicinity will occur until 03Z, with showers in the vicinity from 03Z to 06Z. Thunderstorms will produce wind gusts of 35 to 45 knots at Rawlins and Laramie until 02Z. Otherwise, winds will gust to 28 knots until 03Z, and to 23 knots after 15Z Monday. Nebraska TAFS...Scattered to broken clouds from 8000 to 12000 feet will prevail. Occasional thunderstorms will occur at Scottsbluff and Sidney until 02Z producing wind gusts to 35 knots, with showers in the vicinity at Chadron and Alliance until 03Z. Winds will gust to 22 knots at Sidney after 15Z Monday. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Red Flag Warning until 10 PM MDT this evening for WYZ417-418- 425-428>433. Heat Advisory until 10 PM MDT this evening for WYZ101-102-107- 108-118-119. NE...Heat Advisory until 8 PM MDT Monday for NEZ002-003-019>021-054- 055-095-096. Red Flag Warning until 10 PM MDT this evening for NEZ435>437. && $$ SHORT TERM...GCC LONG TERM...WFOCYS AVIATION...RUBIN