Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/12/19

Area Forecast Discussion
National Weather Service Hastings NE
649 PM CDT Thu Apr 11 2019 .SHORT TERM...(This evening through Friday) Issued at 336 PM CDT Thu Apr 11 2019 Aloft: WV imagery/RAP tropopause analyses and aircraft obs indicated moderately-amplified flow...with a longwave trof was over the Wrn/Cntrl USA...and a ridge over the E Pac. The low that affected the CWA last night and today was along the SD-NEB border near YKN. This low will slowly lift into MN by 12Z/Fri and head to near DLH by 00Z/Sat. In its wake...cyclonic W flow will remain over NEB/KS. Meanwhile...a shrtwv trof will dive down the back side of longwave trof and into the Desert SW. Surface: Filling low pres was over NW IA. This low will cont to fill as it occludes further tonight on its way into Srn MN. This low will weaken into a trof over MN/WI tomorrow. The pres grad here will gradually relax with weak high pres moving in late in the day. Post Mortem: This system definitely fell short of expectations... good from an impacts standpoint...but not from a fcst viewpoint. The performance of the EC was espcly disappointing...track of sfc low...QPF etc. Its low was too deep and too far W. One aspect that over-performed was the amt of hail that occurred with last night`s tstms. See LSR`s for hail/snow. The hail 4" deep btwn Kearney-Gibbon was espcly impressive. After viewing snowplow cams...trimmed most of the counties from the Winter Wx Advy. Left the advy just for where winds were gusting to 45 mph and producing some BLSN. Rest of this afternoon: M/cldy and windy. There are some pockets of -SN lingering here and there. Clds are breaking up over the SW 1/3 of the CWA from Cambridge-Plainville-Osborne. NW winds will cont gusting 30-40 mph with and ocnl G45. Tonight: M/cldy N of I-80 but decreasing clds S of I-80. There is quite a difference btwn the 06Z/12Z NAM vs the 06Z/12Z GFS and RAP regarding the extend of low clds vs clearing. The GFS and RAP are more pessimistic while the NAM runs are more aggressive with the dcrsg clds. Still windy. NW winds 20-30G45. Lows are a blend of the NBM with a little nudge up using the blend of mdl 2m temps. Fri: P-M/cldy along and N of Hwy 6. M/sunny S of Hwy 6. The cold thermal trof will be over the CWA and fcst sndgs show quite a bit of deep CU/SC will form with a sliver of CAPE. These clds will be within the DGZ so expect sct snow shwrs in the morning...changing to rain shwrs in the afternoon where temps will be just warm enough. Still windy as NW winds will be 15-25G35. Temps much cooler than normal with highs in the 30s/40s...coldest along and N of the Platte Rvr. .LONG TERM...(Friday night through Thursday) Issued at 336 PM CDT Thu Apr 11 2019 Aloft: The last 2 runs of the EC/GEM/GFS/GFS-FV3/UKMET mdls cont to fcst the longwave trof to remain over the W thru next Wed. This remains consistent with the 00Z EC ensemble mean. Two more substantial shrtwv trofs will rotate thru the larger trof. The 1st thru the Srn Plns Sat-Sat night and the 2nd next Wed. As this latter trof moves E of the Plns...this will initiate a pattern chg a Wrn rdg/Ern trof and NW flow here. As for the shorter wavelengths...troffiness will remain over the Cntrl Plns Sat...but a shrtwv rdg will arrive Sun with the flow temporarily deamplifying. Heights will then begin falling again Mon- Tue as the trof deepens over the W. That flow will re- amplify. There is considerable uncertainty in what the trof will look like when it ejects into the Plns Tue night into Wed. The 06Z/12Z GFS-FV3 and 00Z/12Z GEM runs are the strongest. NW flow will develop here next Thu as that sys moves into the Ern USA. Surface: Anticyclogenesis will occur over the Plns Fri night-Sat as the high overhead strengthens. This high will weaken Sun. A lee low will form over CO Mon ahead of a cool front fcst to be making its way thru the Wrn USA. Return flow will strengthen with a substantial warm-up...but it will be short-lived as the cool front will cross NEB/KS Mon night. Another low will form on the tail end of that front Tue over the TX panhandle. As that low lifts up the front... that could spread some rain into the CWA Tue night into Wed. The CWA will remain in the cool sector Thu behind a deepening low well to the E. Temps: Much cooler than normal Sat-Sun. A big warm-up Mon- a little warmer than normal. Then dropping back close to or a little cooler than normal next Wed-Thu. Precip: Currently the fcst has nothing Mon night...but there could be sprinkles N of I-80. Tue night into Wed there is potential for some substantial stratiform rain...mainly S of Hwy 6...but gvn the uncertainty aloft...wouldn`t bet on it just yet. For now left thunder out of the fcst. While the 12Z GFS is close to its ensemble mean with the position of the sfc is the further N of the last 2 runs of all the global mdls...suggesting that it`s too far N with its instability. Spaghetti plots 12Z/Wed show the GFS low near SLN while all other mdls are over OK or the TX panhandle. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday) Issued at 633 PM CDT Thu Apr 11 2019 Lower clouds will break up overnight. During the day tomorrow, there will be some cold air cumulus that form. Northwest winds will remain breezy through the period. && .GID WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory until 7 PM CDT this evening for NEZ039- 040-046-060-061. KS...None. && $$ SHORT TERM...Kelley LONG TERM...Kelley AVIATION...JCB
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
757 PM CDT Thu Apr 11 2019 .UPDATE... 756 PM CDT Expect an uptick in rain showers and scattered thunderstorms this evening along and ahead of the cold front as forcing increases ahead of the incoming upper level low. Moderate to briefly heavy rainfall may accompany this narrow axis with SPC analyzed PWATs of 1.1". Afternoon 18z from ILX was fairly dry, and now even the evening soundings which are fairly moist still feature limited instability and even some lingering capping south of the warm front. Lapse rates aloft are still enough for lightning especially as the upper low shifts closer to northeast Illinois and northwest Indiana, and we are seeing an uptick in lightning across northwest Illinois (though still scattered at this point). SPC has lowered to a marginal risk given the aforementioned issues with instability which is our main limiting factor, but given the strength of the wind fields above the surface, a conditional/marginal threat for damaging winds does still exist in any stronger showers and storms, but expect coverage to be isolated. KMD && .SHORT TERM... 330 PM CDT Through Friday... Concerns include the risk for isolated to perhaps widely scattered severe weather late this afternoon through part of this evening, heavy rain/minor flooding risk, and strong winds for parts of the area into the evening and area wide on Friday. Main message for the severe risk is that it appears fairly low and a bit lesser than previous thinking. There are no major changes to forecast thinking for timing of thunderstorms later today into this evening, gradually spreading eastward from 4-6pm west to 10pm-12am east. Wind Advisory headline remains in effect for areas mainly south of I-80 south of the advancing warm front. Seeing gusts into the 40-45 mph range just south of the CWA, so these should spread northward within next few hours. Gusts up to 45 mph will remain possible through just after sunset, so no changes were made to the advisory. Severe threat remains rather uncertain/conditional, however, with timing of any severe storms still appearing similar to previous forecast thinking. Recent AMDAR soundings from MDW and RFD show a pretty stout capping inversion to surface based convection based at 800 mb, with temperatures at +12 to +14 Celsius. ILX 18z sounding showed even warmer temps around +15 Celsius close to 800 mb, so this stout capping will need to be overcome and looks to be a limiting factor. There are steep lapse rates and modest elevated instability above this capping inversion. With steep mid-level lapse rates continuing to be advected northward and strong deep layer south- southwest flow, the capping will be slow to erode. Areas in the far west/northwest CWA closer to better forcing could get some showers and possibly a thunderstorm after 21z, as some lightning is noted in area of showers near the MS River slowly working eastward. Elevated convection here is able to tap into the instability above the capping inversion and this should gradually increase as better forcing arrives from the west. Continued red flags with respect to the potential surface based severe threat include: expansive mid and high clouds limiting insolation and warm sector dew points generally running below guidance thus far in mid to locally high 50s serving to limit SB/MLCAPE as warm front lifts northward (SPC mesoanalysis shows 0 MLCAPE as of about 3pm); and the deep layer shear vector parallel to the cold front orientation. Limited instability combined with extreme deep shear magnitude will likely prevent widespread intense updrafts due to lack of balance of these elements. The unfavorable deep shear vector orientation could also preclude noteworthy forward propagation of line segments. Both of these could prevent a more widespread risk for damaging winds, so message will be potential still existing of isolated to widely scattered severe instances. For perhaps a locally greater severe risk, the warm front continues to lift north at a steady pace (near IL/Kankakee River as of this writing) and the evolving triple point of secondary low pressure lifting northward near MS River could be area to watch over parts of central/north central IL late afternoon/early evening up until about sunset. Cannot completely rule out an isolated tornado in this area despite the generally meager low level moisture. For more details, see the recently issued SPC Mesoscale Discussion. Any severe threat should wane after midnight as available unstable wanes. Overall parallel orientation of shear to boundary and convection ahead of it could tend to yield a transition to more of a heavy downpour/isolated minor flooding risk (for more details see WPC Day 1 Marginal Excessive Rainfall Outlook). If deep moist convection repeatedly trains across the same areas as appears possible with deep layer SSW flow causing slow eastward movement of the convection, there could be isolated 1-1.5" rainfall amounts in a fairly short duration. Showers/some embedded storms will gradually end west to east after midnight into early Friday with cold frontal passage. In the wake of the cold front passage, the occluding and weakening but still seasonably deep surface low will lift north toward Lake Superior on Friday. This will keep the pressure gradient tight across the region between the departing low and weak surface ridging to our south. Cold advection aloft will steepen low level lapse rates and make for more efficient low level mixing. Forecast soundings suggest that advisory criteria (gusts to 45+ mph) will certainly be possible depending on exactly how deep mixing is and efficiency of transporting stronger near to above 40 kt speeds from 900 mb and upwards down to the surface. Another Wind Advisory may be needed, however since there is one in effect for today I-80 south, opted to let midnight shift handle this decision. Friday will otherwise be a quieter day weather wise. Cold advection driven stratocu will fill in across at least the NW 1/2 to 2/3 of the area, keeping temps in the upper 40s to mid 50s under the increasing cloud cover. East central IL counties into northwest Indiana has best chance of reaching the upper 50s. Castro && .LONG TERM... 206 PM CDT Friday Night through Thursday... Main concern in the extended continues to be with a rain/snow mix on Sunday into Sunday evening, with some potential for a period of all snow in some locations across north central IL. Late Saturday night through Sunday night looks to have another strong system impact the area. This will find us more in the cool sector portion of the storm, or at least that continues to be the trend in solutions. This gives concerns for the possibility of numerous hours of wet snow or a wet snow/rain mix in places with even potential for light slushy accumulation. After high pressure brings us a pleasant weather Saturday, this next closed upper low will move northeastward from the Southern Plains. The current forecast track continues to favor the deformation area over the CWA, which along with a stiff northeast wind should support enough precipitation to help offset any daytime warming on Sunday. Still too far in time to say if it is enough to keep a wet snow mix going on Sunday, but enough of a signal to continue this mention in the forecast through the day and into Sunday evening. Highs look to remain below 40 for much of the CWA with this regime, with the exception of areas south of the Kankakee river valley where temps will rise well into the 40s. Again strong wind gusts and potentially lakeside flooding concerns could be raised with this system. Rodriguez/MTF && .AVIATION... For the 00Z TAFs... Main concerns in the latest TAF cycle are: -Near term wind trends with an approaching warm front -Timing a period of VCTS/TSRA -Strong and gusty southwesterly winds on Friday A warm front currently arcs roughly from a VYS to LOT to GYY line and has not made much northward progress over the last few hours. Expect this feature will eventually move through MDW and perhaps right up to ORD before precipitation chances increase this evening. Overall, the TSRA timing has not changed much with the anticipation that overall convective vigor will gradually increase this evening with the approaching of better forcing for ascent. Extended the mention of -SHRA VCTS a bit to account for some trailing stratiform strikes once the main band of convection passes but conditions will steadily improve from west-to-east late this evening and overnight. The other concern will be the increasingly strong and gusty southwesterly winds on Friday. Latest guidance suggests pretty deep mixing up to about 800-750 mb Friday afternoon with unidirectional wind profiles in the cold advective regime. Will indicate 25G35kt in the area TAFs but note that occasional gusts to 40 kts or higher will be possible during afternoon hours. Gustiness will subside Friday evening as the boundary layer begins to decouple Carlaw && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...IN nearshore waters until 3 AM Friday. Small Craft Advisory...IL nearshore waters until 9 PM Thursday. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO