Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/21/21

Area Forecast Discussion
National Weather Service Cheyenne WY
516 PM MDT Thu May 20 2021 .SHORT TERM...(This evening through Saturday) Issued at 216 PM MDT Thu May 20 2021 There are minimal changes from the previous discussion, so it has been attached below. A few strong thunderstorms have begun bubbling up along I-25 warranting a few SPS`s so far this afternoon. Temperatures are in the 70s and 80s with humidities in the teens and 20s west of the Laramie Range and in the 40s and 50s east of the Laramie Range. Winds are generally weak and southerly with the exception of downdrafts from the thunderstorms. Because the winds are generally weak across southeast Wyoming and western Nebraska, the storms will likely not be moving quickly through the afternoon and evening hours. The SPC Severe Weather Outlook includes Cheyenne, Scottsbluff, Douglas, Lusk, and Harrison in a Slight Risk area until 6 AM MDT Friday morning. A few strong to briefly severe thunderstorms are possible through around 11 PM MDT tonight, then all HiRes guidance shows the convection moving northeastward into South Dakota. Main hazards in the strongest storms will be hail between quarter and ping pong size and winds gusting above 58 MPH. Friday... SPC has Cheyenne and the Nebraska Panhandle in a Marginal Risk for severe thunderstorms. The greatest chance for thunderstorms are the afternoon hours until shortly after sunset. HiRes guidance shows the convection Friday being more scattered and less organized than Thursday`s. The winds are stronger than Thursday east of the Laramie Range, so the storms that do form will likely move quickly, limiting the risk for heavy rainfall. Saturday... The unsettled afternoon convection continues, but because of much weaker instability, the chance of any thunderstorms becoming severe is significantly less than Thursday or Friday. With weak upper level winds throughout the day, we will have to monitor the longer lasting storms for isolated heavy rain, especially west of the Laramie Range. ...Previous Discussion... Key Messages: 1) Scattered thunderstorms likely today with isolated strong to severe storms possible this afternoon from 3pm to 10pm. Mainly favored location for strongest storms is along and east of a Douglas to Pine Bluffs line including much of the Nebraska Panhandle. Main severe weather hazards will be 60 mph winds, localized quarter to ping-pong sized hail (high-end), and a brief landspout can`t be fully ruled out. 2) Additional round of showers & storms Friday with a marginal risk of severe storms. Main area of concern will be far east Wyoming into the Nebraska Panhandle. 3) Continued unsettled with scattered showers and general thunderstorms Saturday. Weather Impact Details: Low stratus clouds have developed across West and central NE and along the Laramie Range near Cheyenne this morning. Where the low stratus has not developed, localized areas of fog down to 1 mile visibility is occurring in the southern NE Panhandle as low-level moisture streams in the from south and east. This moisture and eventually realized instability will be one of the key components this afternoon for convective evolution. Regarding the severe potential this afternoon, the SPC has placed far southeast Wyoming and the NE Panhandle in a slight risk of severe storms - let`s break down the evolution possibilities as there are varying degrees of severity potential depending on CAM/global model soundings. Setting the stage - Dewpoints across this area are currently in the upper 40s to near 50 degrees with south to southeast surface winds and PWATs are 0.5" to 0.8" west to east. With modest moisture in place, the next question is lifting mechanism. Synoptically, the much deeper lift remains well west of the region associated with a deepening closed low trough over OR/CA. 500mb flow will initially be quite weak over SE Wyoming and West Nebraska through the early to mid-afternoon at less then 40 knots. Overall dynamic forcing could be slightly aided with embedded H7-H5 shortwave impulses ejecting ahead of the parent low but appears weak per model solutions until 5pm-10pm when wind speeds and wind shear slowly start to increase. 0-6km shear remains weak through much of the day at 30 knots or less until after 6pm when it increases upwards of 35 to 40 knots. Shear vectoring and magnitude will favor multi clustering cells to semi discrete cells initially with some slight upscale growth and/or bowing areas as shear vectors become locally parallel and south to mean wind flow for the northern CWA early to mid evening. However, central and south NE Panhandle shear vectors will remain more perpendicular and assist in more discrete cells support. Lastly, and the big key to the severity today will be the realized instability. There is a wider spread then normal regarding thermo profiles from GFS and various CAMS. On the higher severe envelope would be the NAM3km suggesting 1000-1500 J/Kg MLCAPE and smaller CIN while the HRRR indicates 500-1000 J/Kg and more CIN. GFS soundings side closer to the HRRR with MLCAPE of similar values. Another common factor each have are deeper mixing with some inverted "V" aspects suggesting higher based LCL/LFCs of storms. All combined, isolated to then clustering storms should initiate near 3-4pm into the early evening hours as the cap erodes and slightly greater forcing moves in during the marginally maximized instability period. Will also need to watch for any storms in the CO Plains shifting NE towards southern NE Panhandle. Wind gusts of 60 mph and local quarter to perhaps ping-pong hail on the high end could be possible. Given the higher bases and limited low- level shear, tornadoes are not likely but a brief landspout can`t be fully ruled out. Convection will shift northeast of the region through 10-11pm with a quiet overnight period. For Friday - the closed low will deepen over NV as deeper south H7-H3 flow occurs across the region. Another round of storms will be possible Friday afternoon but strength will be determined by where the instability axis sets up. NAM remains farther west with low-level moisture pool vs. GFS east as lee side low pressure develops along the Front Range. Models are not consistent on convection location but do convect a strong to possibly briefly severe line of storms near the NE Panhandle to just east or just north. Upscale growth is more likely Friday given the deep southerly and unidirectional wind shear. Isolated to scattered showers/storms will also be possible farther west in Wyoming tomorrow as well but the main focus will be on the NE Panhandle and that evolution for stronger updraft potential. Continued unsettled Saturday with at least isolated to scattered showers a general thunderstorms but overall instability looks much lower. May need to monitor for localized heavy rain and training as PWATs increase upwards of 0.6"-1.2" west to east. .LONG TERM...(Saturday night through Wednesday) Issued at 357 AM MDT Thu May 20 2021 The omega block pattern still holds strong across the country bringing changes to our winds, precipitation chances, and temperatures. Starting Sunday afternoon, winds will increase tremendously with pressure gradients increasing between the interaction of a mid-level low and high pressure system to our east. This interaction will bring strong winds to the surface leading to a possible high wind event for our region. Timing is still unclear though it will begin in southeastern Wyoming and by mid-afternoon parts of the central Nebraska Panhandle will be included. Additionally, there are chances of thunderstorms across all cities along with initial QPF accumulations ranging from 0.10-0.30". There is still some dry air which could limit thunderstorm potential and longevity but will continue to monitor this event. Gusty winds will continue into Monday but should subside by Monday evening. Although fuels aren`t ready, Monday`s gusty winds and the combination of low RHs in the Nebraska Panhandle. Overall next week afternoon temperatures will range in the upper 60s to lower 70s for southeastern Wyoming and western Nebraska Panhandle. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 432 PM MDT Thu May 20 2021 Current radar imagery has isolated widely scattered thunderstorms throughout southeastern Wyoming. Seeing reports of wind gusts of greater than 40 knots and radar estimated hail of 1.5 inches on the high end from these convective system. Expecting this trend to continue through this evening with some strong winds from downdrafts from the thunderstorms and periods of pea to quarter size hail possible. Storms should start pushing more eastward into the evening where CAPE values look a bit better. Model guidance has most of these storms dwindling after 3z, with the energy dropping off fairly quickly. Main concern is with the HRRR simulated reflectivity. From 02z to 03z, the HRRR has some decent cell development over the southwestern portion of the Nebraska Panhandle that pushes to the northeast. Will need to watch this time period to determine any severe potentials. Otherwise, VFR and MVFR conditions are expected to continue through tomorrow. && .FIRE WEATHER... Issued at 216 PM MDT Thu May 20 2021 Limited fire weather concerns going into the weekend. Chances of isolated thunderstorms, with a possibility of the thunderstorms being briefly severe, across southeast Wyoming and western Nebraska, mainly east of I-25 Thursday evening until around midnight. Then, more chances of isolated thunderstorms Friday afternoon and early evening east of I-25 with a marginal chance of the thunderstorms becoming severe. Relative humidities across far west Carbon county dip into the lower 20s Friday and Saturday, then into the teens Sunday through next Thursday. Winds will also be picking up early next week. So, the fire weather concerns increase beginning Monday, especially for western Carbon county then spreading into the rest of Carbon county, Albany, and Converse counties throughout the week. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...JSA/LK LONG TERM...AW AVIATION...MD FIRE WEATHER...LK
Area Forecast Discussion
National Weather Service Grand Forks ND
922 PM CDT Thu May 20 2021 .UPDATE... Issued at 922 PM CDT Thu May 20 2021 The convective activity has decreased quite a bit in coverage, and the lightning activity has also dropped. The latest HRRR runs continue to back off on the potential for much shower activity holding together overnight. Therefore dropped any shower chances for the rest of the night to isolated, but not even sure anything will hold together after the next hour or two. The bigger story is now fog, which has spread all the way down to the Interstate 94 corridor in eastern North Dakota and over to the Thief River Falls to Roseau corridor in Minnesota...which is along and north of the surface front. Think the fog will also expand further north overnight, back into the Devils Lake region as well. Think Fargo will be right on the fringe of it, and Bemidji may stay just out of it. Some locations are already down to 2 miles, so dense fog in some areas overnight looks like a possibility. Will continue to monitor the fog to see if it does progress toward the dense side. UPDATE Issued at 707 PM CDT Thu May 20 2021 Still monitoring scattered storms along the Interstate 94 corridor in eastern North Dakota, and from Moorhead to Bemidji in Minnesota. This roughly corresponds to the surface front. There is still some CAPE along and south of this boundary, but effective shear is pretty weak. Also, don`t think the boundary is captured very well by the models. It may actually be a little further south. As cells have been forming along the boundary, they have been lifting northward and weakening. The environment really becomes unfavorable for sustaining these cells north of the boundary. However, like last evening, some of the activity should sustain itself after dark, but most of the thunder should die off. Areas along and south of the Interstate 94 corridor in North Dakota and highway 10 corridor in Minnesota should see the activity shift northward in the next 2 to 3 hours, shifting more toward the highway 2 corridor. Fog has been showing up on observations north of the boundary as well. Not seeing any low visibilities yet, but think after dark the visibilities will drop more. Added in a mention of fog to most areas along the highway 2 corridor overnight (but not the Bemidji to Fosston section, only west of that section). && .SHORT TERM...(This evening through Friday night) Issued at 330 PM CDT Thu May 20 2021 Frontal boundary is well defined now that the other clouds have cleared off. With that sun, CU formed along the boundary from holding near I-94. Other CU upstream into north central SD. This area is in a well heated atmosphere with temps in the low-mid 80s in nrn SD and far srn ND and dew pts in the 60s. So will continue to monitor storm develop along this boundary into the late afternoon. Subsidence behind the departing short wave providing not much in the way of upper level support for convection. Also shear remains very weak so that favored mode is multi-cell with short lived updraft cores at any one time. But with boundary in place there remains some chance for stronger or isold severe storms to form but isold coverage. Non supercell tornado parameters remain rather anemic and lower than yesterday along this zone. Latest fcst shows 2 NSTP values west of Jamestown. SPC meso analysis shows 2-3 NSTP values along boundary in NW MN so will have to watch this area too, though instability is less. Scattered convection will tend to lift north overnight as boundary lifts slowly north. Friday will see warm and humid airmass expand northward to all but far NW fcst area. Friday daytime looks pretty quiet in most of the forecast area as main shower/t-storm coverage is to our west. This will lift northeast into DVL basin Friday evening/night. Isold severe storms would be possible in north central ND in strengthening warm adv zone over the frontal boundary. .LONG TERM...(Saturday through Thursday) Issued at 330 PM CDT Thu May 20 2021 SUMMARY...Multiple chances for showers and thunderstorms headline the long term period as southwesterly flow continues over the area through Tuesday morning. The biggest drivers over the long term is a potent ridge over the midwest and Great Lakes, a few embedded shortwaves, and a broad longwave cutoff low currently spinning over the northwest United States. SATURDAY...Ensemble guidance has a solid handling on a shortwave trough progressing through a high amplitude wave over the midwest. A strong cold front is expected to slowly trudge through the area. Ahead of this shortwave, modest elevated instability and very moist profiles are evident, shown by steep lapse rates aloft and ensemble forecast percentiles at or above the 99.5th percentile for PWAT. As such, showers and thunderstorms appear probable on Saturday. Temperatures behind the cold front are expected to be in the 50s while ahead of the front, temperatures could get as high as the mid 80s. How quickly this front moves through will gauge afternoon highs Saturday. SUNDAY...Another less prominent shortwave will ride the ridging over the midwest, bringing another chance for showers and possibly a few thunderstorms, although confidence is much less given weak forcing. MONDAY...Confidence is high on at least meaningful precipitation along the western boundary of our CWA. A rather prominent cutoff low, currently spinning over the northwest US and locked up by the downstream ridge, will finally push through as ridging begins to deamplify and push eastward. Given the proximity of the low to the CWA and the degree of forcing overspreading much of North Dakota, confidence is high in showers and thunderstorms over the western part of the CWA, especially along the Devils Lake area. Ensemble guidance has been notably dry in QPF despite the strong forcing, primarily due to dry air advection in the lower levels. Big question regarding this event will be the degree of dry air advection and how much forcing makes its way into our CWA. Cluster analysis appears to indicate very solid agreement in location of the low being rather far west (over eastern Montana), so there is high confidence in the highest QPF values being further west, outside the CWA. Still, areas that didn`t receive rain within the current event appear to have a solid chance at making up the difference on Monday. TUESDAY THROUGH THURSDAY...As the cutoff low spins back into the flow, cooler temperatures can be expected to develop on Tuesday and Wednesday. Temperatures will fall into a cooler than normal range in the 60s and low 70s before ridging redevelops and temperatures slowly rebound toward the end of the period. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 707 PM CDT Thu May 20 2021 It looks to be the tale of two areas overnight. For Fargo and Bemidji, after some early showers and storms, the activity should end and conditions should remain VFR. For KDVL, KGFK, and KTVF, low clouds and fog will hold tough overnight into Friday morning. Not sure how low the visibilities may get, so stuck more in the MVFR range for now. On Friday morning, the boundary will push back northward, helping to scour out the low clouds and fog. Timing is pretty hard to nail down, so just went with possible trends for now. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. $$ UPDATE...Godon SHORT TERM...Riddle LONG TERM...Perroux AVIATION...Godon
Area Forecast Discussion
National Weather Service Goodland KS
549 PM MDT Thu May 20 2021 .SHORT TERM...(This evening through Friday night) Issued at 306 PM MDT Thu May 20 2021 Overview: SW flow aloft will prevail over the Tri-State area.. downstream of an amplifying upper level trough over the Intermountain West. Today-Tonight: Low-level southerly flow continues to strengthen over northwest KS this afternoon.. as the MSLP/H85 height gradient tighten on the eastern periphery of a deepening lee cyclone in Colorado. At NWS Goodland.. southerly winds were sustained at 30-35 mph gusting to 40-45 mph at 21Z. Forcing: Aside (perhaps) from small amplitude perturbations in SW flow aloft.. forcing this afternoon is largely confined to low- level convergence invof the lee trough/cyclone in CO.. and SSE upslope flow along portions of the Palmer Divide. Thermodynamics: Recent mesoanalysis data indicates a disconnect between the richest low-level moisture (H85 dewpoints ~13C in northwest KS) and steepest mid-level lapse rates / renewed EML (8-9 C/km in CO) -- with mlcape values ranging from 500-1000 J/kg and a small amount of convective inhibition in eastern CO, where diurnal Cu is noticeably absent in visible satellite imagery. Expect convective inhibition to increase everywhere late this evening.. as insolation wanes. Shear: Effective deep layer shear presently on the order of 25-30 knots is anticipated to increase to 35-45 knots by ~00Z. Isolated convection developed ~30 miles NNW of Limon, CO around 20Z. As of 2130Z, one updraft persists.. This updraft has gradually strengthened.. and is apt to continue strengthening as it progresses NNE into increasingly rich low-level moisture (amidst strengthening deep-layer shear) in northeast CO, which.. is in close agreement to simulated reflectivity forecasts via the latest runs of the HRRR.. which more-or-less confines development (and severe weather potential) to this particular storm.. as it tracks NNE to NE along and south of I-76 between 22-02Z. Aside from (perhaps) a glancing blow to northwest portions of Yuma county, severe weather is otherwise unlikely. Fri-Fri night: Thermodynamic conditions will become increasingly favorable for convective development in this time-frame.. and simulated reflectivity forecasts via the latest runs of the HRRR and NAM NEST suggest that numerous updrafts will develop around peak heating.. invof a strengthening /N-S oriented/ convergence zone in CO. With southerly flow present throughout the lower-mid troposphere.. initially isolated updrafts are anticipated to quickly grow upscale into a N-S oriented cluster that subsequently progresses slowly east toward the CO/KS border.. dissipating with loss of insolation AOA sunset Friday evening. Damaging winds are anticipated to be the primary severe threat, though large hail is certainly possible with initially discrete updrafts -- prior to upscale growth into a cluster. .LONG TERM...(Saturday through Thursday) Issued at 114 PM MDT Thu May 20 2021 Closed upper low will start the period over the Great Basin then lift into the northern Rockies Sunday night and into central Canada by Tuesday. The local area will be under a broad south to southwesterly flow aloft on the southern side of this system. Convective chances on Saturday will be tied to a surface trough/dry line forecast to be oriented along/near the Colorado and Kansas border area. 0-6km mean winds should result in a north to northeast storm motion, so some question how far east storms will progress before fading after sunset. Instability and shear parameters not particularly impressive, so would expect only marginal risk of severe storms on Saturday. Pattern changes little on Sunday, with isolated/scattered storms initiating once again in eastern Colorado along the surface trough, with perhaps weak support aloft from a shortwave embedded in the southwesterly flow. Shear/instability parameters slightly better compared to Saturday, with an uptick in shear as the flow increases aloft due to the closer proximity to the upper low. Storm motions again north/northeast which will limit eastward progression of storms through the evening hours. As the upper low pulls away early in the week, associated surface front will become nearly parallel to the upper flow and become stationary in/near the forecast area Monday and Tuesday, possibly sinking just south by Wednesday. Frontal boundary will be favored location for convective initiation each day, but difficult to pin down exact location at this time range. Some weak forcing aloft will be present Monday and Tuesday with embedded shortwaves in nearly zonal flow. Deep layer shear is best on Monday, with up to 50 kts forecast, and may have the most potential for severe storms, decreasing a bit to around 40 kts on Tuesday. Thunderstorm chances continue Wednesday and Thursday as the upper flow turns southwesterly ahead of the next low digging into the Great Basin. Deep layer shear will be at least 40 kts both days, sufficient for organized convection and severe storms. Only question is coverage with relatively weak forcing and location which will depend on subtle mesoscale boundaries. Lack of predictability on both accounts will result in POPs in the 20-30 percent range. Temperatures throughout the period will be above normal, with highs mostly in the 80s and lows mostly in the 50s. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 546 PM MDT Thu May 20 2021 VFR to IFR conditions forecast for the TAFs. The gusty winds will decline some during the night. However a strong LLJ will be overhead, so am expecting LLWS despite the breezy surface winds. Around 9z low stratus will move in from the east, impacting KMCK. Current data is suggesting this will be a mix of MVFR and IFR ceilings. At this time will forecast the worst as this seems more reasonable give the soundings and the rather high dew points. KGLD should be west of the stratus. The LLWS and stratus will end around 15z. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ SHORT TERM...VINCENT LONG TERM...024 AVIATION...JTL
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
722 PM CDT Thu May 20 2021 .SHORT TERM...(This evening through Friday night) Issued at 317 PM CDT Thu May 20 2021 The highly amplified upper level pattern continues over the lower 48 states with a blocking upper level ridge over the eastern seaboard and a digging trough over the western CONUS, promoting meridional flow over the central states. This pattern continues to usher in additional deep layer moisture (PWATs over 1.25") along with warmer low-to-mid level temperatures which will remain over the Upper Midwest into the weekend. The surface pattern also has had and will have little variation through the next 36 hours, with high pressure along and east of the Appalachians and a quasi-stationary frontal boundary extending SW from southern Hudson Bay across northern MN, the Dakotas and the northern Rockies. The surface front to the west is expected to slowly shift eastward through the next 24-36 hours, such that a weak low pressure center is expected to develop along the front over eastern ND with the cold front snaking more southerly through the Plains by Saturday morning. With little change in the environment over the Upper Midwest, this means continued warming and moisture advection, leading to additional instability. However, the lack of impressive lapse rates will cancel out overly high CAPEs but with just modest jetting combined with several positive vorticity centers rotating north to northeast around the large eastern CONUS ridge into the northern- tier states tonight through Friday, there remains the potential for isolated strong/severe storms along with pockets of heavy rain. SPC maintains a Marginal Risk for the entire coverage area for tonight and for eastern portions on Friday which is very reasonable given the narrow north-south oriented area of forcing on the immediate western periphery of the ridge. Any and all convection that is ongoing this evening will diminish a bit in coverage/intensity going into the nighttime hours due to loss of diurnal heating. However, HRRR/SREF suggests another surge in rainfall from northeastern IA into eastern MN/western WI overnight. This additional moisture may well also aid in fog development through daybreak. As the forcing mechanisms aloft rotate away from the WFO MPX coverage area during the day Friday into Friday night, this will allow for a slow and partial clearing of cloud cover away from the area. The main mechanisms for forcing on Friday will be diurnal heating once again and residual boundaries from overnight convection. However, the loss of daytime heating and exiting of more appreciable forcing for Friday night will spell a dry forecast. Temperatures will again slowly warm over this short-term period. Highs will nudge up to the upper 70s to lower 80s on Friday, following highs roughly 5-10 degrees cooler than that this afternoon. Lows will also creep upwards, from the lower 60s tonight to the mid 60s Friday night. .LONG TERM...(Saturday through Thursday) Issued at 317 PM CDT Thu May 20 2021 The long term period is split into two distinct parts, the first being the stagnant pattern bringing moisture and warmth into the northern plains due to a ridge over the SE US and troughing near the west coast, and the second being after the western trough pushes northeast through the area which will shake up the overall environment through the rest of next week. The upper level low over the western CONUS continues to eject shortwave energy over the area, resulting in chances for showers and storms for most of the period except Saturday. A brief period of dry air will allow for lower cloud cover and lack of precipitation on Saturday, which will lead to the warmest overall temperatures we have seen so far this year with upper 80s to low 90s Saturday afternoon. Just how much cloud cover will determine what our temperatures end up being, with NBM still sticking along the 50th percentile in the upper 80s. 90th percentile is still in the low 90s, showing the uncertainty still present in the forecast. Isolated convection is still possible if we get enough mixing to overcome any capping that is present, however with no forcing we would rely on daytime heating on Saturday. Shower and storm chances increase Saturday night into Sunday morning as another shortwave ejects from the upper level low to our west, with chances improving even further Monday as the system begins to move northeast dragging a cold front across the region Monday evening through Tuesday morning. Right now, forecast soundings are pointing more towards a heavy rain event than a severe weather event, with PWAT values near the climatological max for late May, not surprising considering the several days of moisture funneling northwards into the region. This combined with enough upper level support should keep any potential for severe weather isolated, with heavier rainfall the larger threat. Conditions look to cool by Wednesday and Thursday back near 70 for highs as a ridge builds into the area in between systems, with the signal being another trough building behind the ridge heading towards the end of next week which could signal further rainfall potential. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 722 PM CDT Thu May 20 2021 Next wave of rain is quickly gathering steam over IA and will impact eastern MN/western WI tonight. Though the CAMs are a little slow with their timing of this wave, they are in good agreement with it impacting MSP/MKT/RNH/EAU. For MSP/MKT, it`s the 4z to 10z wind that looks best for rain, with those rain chances lingering out to about 16z in WI. Some TS is possible, but there`s been hardly any lightning in this plume of moisture between MN/WI and TX/LA all day, so kept TS mention out of TAFs due to low probabilities. A little less confidence on cig heights for tonight, with the CAMs showing pretty good spread in heights, though confidence is high that the rain areas will drop to at least MVFR levels tonight, with IFR cigs certainly possible as well. Much more uncertainty west of the rain, with anything from clearing skies (HRRR) to redeveloping MVFR/IFR stratus (LAV) being possible. Given how moist the boundary layer is, it`s hard to go quite as optimistic as the HRRR at a place like AXN. For Friday, the moisture plume shifts east, taking additional rain chances east of our area as well. The main question for tomorrow is how much do we see skies break out, but west of I-35, there should be a good chance at seeing some sun by the afternoon. KMSP...Confidence is high that it will rain tonight at MSP, especially in the 5z to 10z window. There may also be a rumble of thunder or two in this timeframe, but not enough to include in the TAF at this time. Most guidance shows cigs dropping into IFR levels between 8z and 10z, which makes sense given the expected rainfall. There`s a high degree of uncertainty on when the IFR cigs depart. We could see MVFR or better as early as the rain moving out (around 12z) or we could see it linger for much of the morning. Split the difference for now. After this wave moves away Friday morning, confidence is high in the rest of the TAF period being dry, with VFR conditions arriving in the afternoon. /OUTLOOK FOR KMSP/ Sat...VFR. Wind SW 10-15 kts. Sun...SHRA/TSRA/MVFR likely, mainly p.m. Wind SW 5-10 kts bcmg SE. Mon...SHRA/TSRA/MVFR likely, mainly p.m. Wind SW 10-15 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ SHORT TERM...JPC LONG TERM...TDH AVIATION...MPG
Area Forecast Discussion
National Weather Service Marquette MI
749 PM EDT Thu May 20 2021 .SHORT TERM...(This evening through Friday) Issued at 359 PM EDT THU MAY 20 2021 GOES water vapor imagery and RAP analysis show a persistent highly amplified upper-level pattern over the CONUS this afternoon with a trough over the western CONUS and a ridge centered over the Ohio and Tennessee River Valleys and a consistent southerly stream of Gulf moisture into the Western Great Lakes between these features. Scattered showers have been confined to mainly the western third of the fcst area this afternoon, closer to the axis of higher dewpoints (in the mid 60s0, best 825-850 mb moisture transport and pwats of nearly 1.6 inches. Temps have been in the 60s west and downwind of the Lake Mi shoreline, but have been mostly in the 70s elsewhere under mostly cloudy skies. Tonight into Friday, mid-level flow axis begins to tilt a bit more from S-N to SE-NE as the SE CONUS ridge begins to retrograde just a bit west, which will allow a wave and associated forcing to move through western Upper Michigan. Models show a more consistent signal for rain to move into western Upper Mi late tonight into Fri morning with increasing 850-700 fgen in right entrance region of jex max associated with the shortwave. It`s uncertain how much of the rain from this band will hold together into central zones Fri morning as fgen will be weakening by that time. Expect only isolated to scattered coverage of showers during the day on Friday over the central counties. Model consensus suggests locations over the west could pick up nearly .5 inch from the band, central counties will be more in the .1 to .25 inch range and out east less than .1 inch. NAM and HRRR soundings indicate anywhere from 100-300 j/kg MUCAPE over the west so will continue to mention isolated thunderstorms over the western cwa, including western Lake Superior late tonight into Fri morning. A record high minimum will likely be broken here for May 20 at NWS MQT as the record is 57F in 1977 and we probably won`t get below our current low for the day by midnight which was 63F early this morning. Expect lows tonight under mostly cloudy skies to be in the low to mid 60s except mid to upper 50s readings east downwind of Lake Mi. Highs Friday will be mainly in the lower to mid 70s with some 60s readings along Lake Mi and maybe over the tip of the Keweenaw under mostly cloudy skies. .LONG TERM...(Friday night through Thursday) Issued at 421 PM EDT THU MAY 20 2021 The long-term period looks quite variable. On the large scale, upper- level ridging will persist into the middle of next week over most of the eastern CONUS. However a shallow front will lead to some wild temperature swings this weekend. Most days will feature at least a chance of rain as the pattern remains unsettled, although large- scale forcing for ascent is hard to come by so it`s tough to say with any confidence where, when, and exactly how much rain will fall. Starting off Friday night, a weak "cold" front/wind shift will be moving across the U.P. from west to east. The temperature gradient will be negligible with the passage of this subtle front. If anything, lingering clouds and showers because of it will keep temps quite warm for overnight lows, even on the "cool" side of the boundary. Most areas will see temps stuck in the mid 60s for lows leading to some uncomfortable sleeping weather. On Saturday, that weak front moves out of the area leading to clearing skies. Despite the front Friday night acting like a cold front, it`s actually more like a dry front. PWATs are expected to drop from around 1.75" ahead of it to around 1.0-1.25" behind it. With this somewhat drier air moving in and sunshine returning on Saturday, it will be hot as we start mixing down 850 mb temps that will be around 13 C to start the day and rise to around 17 C by the evening. There will be enough of an offshore wind to keep the Lake Superior lake breeze locked to the shoreline and allow the heat to make it all the way to the water`s edge. Highs will likely be in the low to mid 80s. Will note however that the NBM init of upper 80s seemed too warm given the modeled 850 mb temps, even assuming deep mixing. The exception to all of this will of course be along the Lake Michigan shoreline where the southerly wind will advect cooler air onshore and hold temps down in the mid 60s to low 70s. A stronger cold front is expected to approach the area late Saturday night. It appears instability will be limited but there could be enough MUCAPE for a few thunderstorms. However the majority of the forcing for ascent will remain north of Lake Superior until very late in the night, by which point instability should have waned enough to prevent thunderstorms. Behind the front, there will be an appreciable drop-off in surface temps on Sunday. Not only is there some impressive shallow CAA with this front, but winds become northerly and advect the cool marine layer onshore which will make for even cooler temps. Temps will struggle to get out of the 40s for highs along the Lake Superior shoreline, and may remain stuck in the 50s even far inland. The front will become west-east oriented, stall out, and weaken on Sunday. The model consensus is for it to stall out in Wisconsin leaving the entire U.P. on the cool side. With plenty of moisture to the south, and low- to mid-level moisture convergence along the boundary, there will likely be periods of showers throughout the day Sunday. There could be up to a few hundred J/kg of elevated CAPE for weak embedded thunderstorms, but for now have opted to remove thunder mentions on Sunday. This front will push back north on Monday leading to a warming trend. However, with high PWATs pushing back north into the area, and messy flow aloft with numerous short waves, showers and thunderstorms are a good bet on Tuesday. Despite 850 mb temps on Tuesday probably being warmer than on Saturday, clouds and precip will likely hold surface temps down in the mid 70s to around 80. Models and their ensembles are in good agreement that by Wednesday a strong mid-level wave and associated surface cold front will move into the Upper Great Lakes leading to much cooler temps for Wednesday and Thursday. Some frost could even be possible Wednesday night. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 749 PM EDT THU MAY 20 2021 Periodic shra will affect KIWD/KCMX for much of this fcst period. Although heavier shra could drop conditions to IFR at KIWD tonight, expect prevailing MVFR for much of the night followed by a period of IFR Fri morning. Conditions should improve back to MVFR by aftn. At KCMX, VFR conditions should prevail this evening with a period of LLWS also expected. Conditions should then fall thru MVFR overnight to IFR Fri morning. Any heavier shra could drop conditions to IFR. Improvement to MVFR will occur early Fri aftn with perhaps further improvement to VFR by late aftn. At KSAW, VFR conditions are likely to prevail tonight with much of the shra activity passing by to the w. Increasing low-level jet will lead to LLWS by late evening, then ending by mid morning Fri. MVFR conditions should prevail at KSAW during the day Fri. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 359 PM EDT THU MAY 20 2021 Winds 20 knots or less are expected through much of the fcst period. With higher dew points remaining over the lake for the rest of the week, and multiple chances of rain expected between now and the weekend, areas of fog are expected to develop and then persist for several days and just drift around the lake until dewpoints diminish. There`s a good bet it will be dense at times. The best chance for fog to diminish and winds to increase will be with a cold fropa late Saturday night/early Sunday as north to northeasterly winds could gust up to 30 kts. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... Dense Fog Advisory until 8 AM EDT /7 AM CDT/ Friday for LSZ162- 263. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...RJC AVIATION...Rolfson MARINE...Voss
...Updated Aviation Forecast Discussion...

.DISCUSSION... Issued at 333 PM CDT Thu May 20 2021 Temps struggling to climb to forecast highs this afternoon. Have seen very little change in temps over past six hours under low overcast deck at about 2500 feet. Have lowered expected highs as a result. A few weak storms have developed west of here were the cu field eroded this morning and temps have been a bit warmer. Here in eastern Nebraska, showers have shown little propensity for upward growth and no lightning as of 20:30Z. HRRR has been consistent with keeping highest dBZs in southwest Iowa through the afternoon through about 3Z. Lapse rates are unimpressive (less than 7C/km) with CAPE less than 1000J/kg generally speaking. Convection won`t be towering, limiting the hail threat, but with any sustained storm in the low LCL environment, Iowa finds itself part of a long ribbon of the central CONUS with a small tornado threat. Precip transport and PWAT values are in the 99th climatological percentile across parts of Iowa and areas south of here. Flash flood watch has been posted for parts of Missouri and Kansas, but believe the significant QPF remains too far south to affect this CWA. Expected rainfall for extreme SE Nebraska / SW Iowa currently expected to remain less than 0.50", though a quickly moving downpour could produce a bit more. Friday brings mostly dry conditions as IVT focus shifts east. With some sun filtering through a scattered cu field, expect widespread low to mid-80s... seasonally a bit warm for May`s second half. For many locations, these will be the first 80s in almost three weeks. As the 500mb high meanders *west* on Saturday, scattered convection is possible (though not probable) in the CWA`s southern half. Generally dry conditions, though, persist through the weekend for the entire area... as do the low to mid-80s. Anticipating a cold front early next week with the western CONUS`s mid-level trof pushing into the country`s mid-section. This will provide focus for another round of convection and open the door to cooler conditions by mid-week. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 627 PM CDT Thu May 20 2021 There are ongoing thunderstorms near KOFK, while there are rain showers near KOMA and KLNK. Thunderstorms aren`t expected to become severe and we haven`t received any hail reports from that area. Rain showers along the Missouri River haven`t displayed much of a convective element thus far and at this point, we`re not expecting them to do so. Outside of precipitation, ceilings are expected to lower to IFR criteria at or after 06Z. Ceilings are expected to stay at IFR for a few hours and should lift to MVFR after 12Z. Winds are forecast to remain southerly and above 10 kts for the TAF period. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Nicolaisen AVIATION...Fajman
Area Forecast Discussion
National Weather Service Phoenix AZ
506 PM MST Thu May 20 2021 .UPDATE...00Z Aviation Discussion. && .SYNOPSIS... An approaching weather system will lead to breezy to locally windy conditions through Friday and cooler temperatures into the weekend. The weather system will also bring increased cloudiness this afternoon into early Friday morning and likely some lower desert sprinkles and mostly light high elevation rainfall tonight. Lower elevation high temperatures will fall well below normal into the 80s for Friday and Saturday before warming back to or just above normal readings starting early next week. && .DISCUSSION... Current METSAT and upper air RAP H5 analysis shows the large low pressure system pushing well through the Pacific NW along with its strong jet streak and PVA anomalies. Semi-moist W-SW flow was noted aloft as a swath of high clouds and elevated WV was advancing into the region from the W-SW in advance of a EPAC shortwave disturbance south of the main low. Current ACARs soundings exhibit the W-SW flow aloft with indications of upper- mid level moisture advection near 600 mb. Light radar returns were seen moving across N Baja. The column was stable and PW was on the rise and passing through 0.5". Today expect a degree or 2 cooler than yesterday with a highs in the upper 90s to 100. The upstream, strong closed low pressure system will continue to dig towards the region through the Western US through Saturday with the base of the trough settling over N Baja. The system will usher in cooler temperatures and breezy to windy conditions, especially out west where patchy and lofted blowing dust is a concern through tomorrow. As a result a wind advisory remains in effect for parts of SE CA including Imperial Cty, in the west CWA. There is also a Red Flag warning for this afternoon and evening for the Lower Colorado River valley for critical fire weather conditions developing there. A pre-system weak PVA disturbance with a moderate IVT moisture plume slips in around the base of the system tonight and provides our slight chance of rain late tonight and the first part of Friday morning. As far as QPF goes the GFS and GEFS now features a modest amount of QPF for the E CWA as they get a better handle on that moderate IVT moisture plume. HREF family members agree on mostly light rain with the next system from this evening to the first half of Friday morning. No real outliers today, although the HRRR became the most bullish on some embedded heavier showers late tonight in and around the NE Phx valley. Forecast soundings and HREF CAPE forecasts indicate stable conditions and almost no CAPE due to the offset position of the low and colder air displaced well to the NW. Also theres a bit more moisture in the lower mid levels now extending down to near H7 and fairly dry below that. The result now is at least for some low QPF for some models and WPC. For most of Friday and into the weekend the system will feed drier air into the region as POPs quickly and substantially diminish west to east. Highs for the weekend will fall to near 10 degrees below normal in the low 80s out west to the mid to upper 80s around Phoenix. The clusters and ensembles analysis/forecast agree that the low will begin to eject by mid weekend and into early next week towards the northeast into Montana in all scenarios. As it does heights will recover and high temperatures will warm back up to near normal in the upper 90s by Mon-Tue. Some weak dry cyclonic troughing will then dominate the region well into next week. && .AVIATION...Updated at 0005Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: West-southwest winds will increase in speed through this evening. Gusts will peak between 23-06Z potentially exceeding 30 kts at KPHX & KDVT, while only reaching the mid-upper 20s at KIWA & KSDL. Gusts are anticipated to taper after 06Z but winds will stay elevated through the overnight hours and likely not transition to an easterly wind but be more southerly. Gusty day again tomorrow afternoon but wind gusts should remain slightly below today`s levels. Clouds will continue to increase in coverage and lower through the period as we are likely to see a BKN deck around 100 by 06Z. Around this time, there could also be a layer of clouds near 7 kft. Cloud cover will start to improve as we head into the morning and afternoon hours tomorrow. Low chances (10-20 percent) for isolated showers and virga across the valley from 07-12Z before drier air pushes in. Due to lower confidence on coverage, leaving out of TAF package at this time. Southeast California/Southwest Arizona including KIPL and KBLH: Winds will be the primary aviation weather concern through the TAF period. Wind gusts as high as 35 kts at KIPL and closer to 40 kts at KBLH through 04/05Z. At KIPL, gusty conditions will be present for the remainder of the TAF period, with gusts dropping closer to 25-30 kts overnight before increasing close to 30-35 again tomorrow afternoon. At KBLH, gustiness will subside after midnight, but increase again tomorrow afternoon with gusts close to 30 kts. These gusty winds will cause periods of blowing dust and reduced visibilities. Lofted dust may also cause slantwise visibility issues. && .FIRE WEATHER... Sunday through Thursday: Very dry conditions with periods of breezy winds are expected through the period. A dry, weakening weather system departs on Sunday leaving lighter winds, but with some afternoon gusts to 20 mph still possible Sunday through Wednesday. Min RH levels will stay near 4-8% through the period, while overnight Max RHs will mostly fall within 15-30%. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Red Flag Warning until 8 PM MST this evening for AZZ131. CA...Red Flag Warning until 8 PM PDT this evening for CAZ231. Wind Advisory until midnight PDT tonight for CAZ563>567. Wind Advisory until 9 AM PDT Friday for CAZ562. && $$ DISCUSSION...Sawtelle AVIATION...Feldkircher FIRE WEATHER...Sawtelle/Kuhlman
Area Forecast Discussion
National Weather Service Shreveport LA
1000 PM CDT Thu May 20 2021 .UPDATE... We have extended the Flash Flood Watch through 7AM Friday. && .SHORT TERM.../Tonight/ Areas that have been rain-free during the afternoon are seeing the bulk of showers and some occasional thunderstorm activity focused over western LA. This activity is stretching from Toledo Bend Country up into NW LA and the Shreveport and Bossier metro area right now with another flash flood warning posted until 11pm over Toledo Bend country. Rainfall rates continue to run right along FF guidance values for possible flooding with a few good hours left in the current reflectivity that will continue to more or less train up the I-49 corridor toward until well after midnight. This more than covers the current activity and will give the night shift theopportunityy to determine if all or any part of this Watch that may be needed to be carried forward in our Friday forecast. We made some subtle changes to pops and weather for the night with no other changes needed at this time. /24/ && .PREV DISCUSSION... /issued 717 PM CDT Thu May 20 2021/ AVIATION... For the ArkLaTex terminals weak upper low will keep showers with an isolated thunderstorm possible through midnight with activity in Toledo Bend country lifting toward KSHV now and KTXK later on this eve. Generally, S/SE winds will prevail around 10KT and maybe a little gusty around these torrential downpours. Friday will see more scattered showers and isolated thunderstorms with coverage diminishing over the weekend as the low lifts northward. High pressure aloft will dry us out for a couple of days. /24/ PREV DISCUSSION... /issued 226 PM CDT Thu May 20 2021/ SHORT TERM.../now through Friday night/ A lingering upper level trough axis to our west currently is helping spur deep and moist low level southerly flow across the Four State region with the focused moist axis being sharpened by a ridge of high pressure aloft growing well to our E/NE. Most of the showers today in our region have been confined thus far in the Arklamiss and in east TX, but we anticipate the coverage of showers and embedded thunderstorms will increase across the rest of the Four State region (specifically, the Arklatex and northwest and central LA) through the remainder of the afternoon as patches of filtered sunshine has allowed for more destabilization. Deep layer wind shear over these areas is not impressive, but low level wind shear is just enough to not be able to rule out a brief and relatively weak tornado with any robust and surface-based updrafts that take shape. Rainfall amounts thus far today have not been impressive and the current showers are not training over the same ground in such a way to be concerned about immediate flooding manifesting. However, recent HRRR runs suggest a potential corridor of training thunderstorms taking shape late this afternoon and into the evening right up the I-49 corridor. Owing to this potential, and the associated flood risk such a scenario would entail, we have decided to extend the Flash Flood already in effect for the bulk of the area through 6Z tonight. After that time we only anticipate patchy showers to be remaining. Otherwise, anticipate lows tonight mainly in the mid to upper 60s with mostly cloudy skies. Model consensus for tomorrow depicts an upper level low forming from energy pinched off from the base of the current trough to our east to be focusing deep southeasterly moisture transport a little farther southwest. All areas will be close enough to the continued rich moisture transport regime to have decent chances of afternoon showers and embedded thunderstorms, but this activity will be very likely in southern zones (especially across Deep East TX). Current indications from the Weather Prediction Center are that the flooding potential should mainly be limited toward the SE TX and SW LA coast tomorrow. However, there is still some isolated flash flooding concerned over at least our SW third of zones where spotty 1 to 2 inch rain amounts on pretty well saturated ground could cause at least a few minor issues. Currently we do not anticipate extending the current flash flood watch past midnight tonight, although it is not inconceivable the overnight shift may have to reissue a small flash flood watch focused on these southwest zones for tomorrow. Otherwise, expect mostly cloudy skies to again hold high temperatures mainly in a range from the upper 70s to lower 80s. These values are below normal for late May, but plenty of humidity will keep conditions from being truly pleasant. Tomorrow night lingering showers and storms will become more confined toward Deep East TX by late in the evening hours with low temperatures again in the 60s and some patchy late night fog cannot be ruled out. /50/ LONG TERM.../Saturday through Wednesday Night/ Upper-level ridge to retrograde westward across the Deep South bringing drier conditions across much of the region through much of the long term period. However, locations on the western periphery of the ridge, which would include portions of east Texas, can expect scattered afternoon convection through Monday. With the majority of the long-term period dominated by upper-level ridging, subsidence aloft will bring warmer temperatures to the region. Afternoon high temperatures will climb into the upper 80s across areas that are in closer proximity to the center of the ridge which would include mainly south-central Arkansas and northeast Louisiana. Slightly cooler temperatures in the lower 80s will prevail across east Texas and southeast Oklahoma. Overnight lows will average in the upper 60s to around 70 each night. Otherwise, A slow moving weak upper-level trough to swing east across Texas bringing increased convection areawide from Tuesday night into Wednesday. /05/ && .PRELIMINARY POINT TEMPS/POPS... SHV 68 80 65 84 / 60 70 40 20 MLU 66 83 64 86 / 40 50 10 10 DEQ 67 80 65 82 / 70 60 40 20 TXK 68 80 66 82 / 70 60 40 20 ELD 64 83 63 86 / 50 40 10 10 TYR 69 80 67 79 / 30 70 50 70 GGG 67 79 65 80 / 50 80 50 50 LFK 68 78 67 79 / 40 90 60 70 && .SHV WATCHES/WARNINGS/ADVISORIES... AR...Flash Flood Watch until 7 AM CDT Friday for ARZ050-051-059>061- 070>072. LA...Flash Flood Watch until 7 AM CDT Friday for LAZ001>005-010>013- 017>020. OK...Flash Flood Watch until 7 AM CDT Friday for OKZ077. TX...Flash Flood Watch until 7 AM CDT Friday for TXZ096-097-108>112- 124>126-136>138-149>153-165>167. && $$ 24/50/05