DAY1SVR: Day 1 Convective Outlook

Msg # 1161 of 2431 on Fidonet Weather Echo
To: WX-STORM@LISTS.ILLINOIS.E, From: COD WEATHER PROCESSOR
Time: Tuesday, 6-02-20, 4:34
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ACUS01 KWNS 021634
SWODY1
SPC AC 021632
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1132 AM CDT Tue Jun 02 2020
Valid 021630Z - 031200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHERN
PORTIONS OF MN/WI INTO WEST-CENTRAL LOWER MI...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS EAST-CENTRAL WY TO
THE WESTERN NE PANHANDLE...
...SUMMARY...
Severe thunderstorms are most likely across parts of the Upper
Midwest centered on southern portions of Minnesota and Wisconsin
beginning after 4 PM CDT, eventually spreading into at least Lower
Michigan overnight. Damaging to destructive winds and large hail
will be the primary hazards.
...Upper Midwest...
Primary changes are to add a significant severe wind area within a
portion of the category 3/Enhanced risk for the potential of wind
speed damage estimates exceeding 75 mph and to expand category 3
severe risk into west-central Lower MI.
Convective initiation is expected by late afternoon as low-level
convergence strengthens along a surface front extending southwest
and east-northeast of a cyclone expected to be over southeast SD.
The NAM appears overdone with mean mixing ratios and resultant progs
of extreme buoyancy given 12Z observed soundings and GOES PW
imagery. RAP/ARW-SREF guidance and 16Z surface obs suggest a hot and
well-mixed boundary layer will instead be prevalent. A plume of
MLCAPE from 2500-3500 J/kg is anticipated by peak heating.
With a low-amplitude shortwave trough moving east-southeast from
Manitoba across northern Ontario, the peripheral belt of moderate
mid-level westerlies will largely remain north of the MN/IA to WI/IL
border area. Thus, the most likely corridor for a few initial
supercells should be confined to southern MN with some risk for very
large hail. Upscale growth into outflow-dominated clusters appears
probable, increasing the potential for severe wind gusts across
southeast MN into southern WI this evening. Given the steepness of
low to mid-level lapse rates and a strongly unstable air mass,
potential will exist for isolated significant severe gusts as well.
The modest deep-layer wind fields appear to be a limiting factor to
a more widespread/organized damaging wind risk. However, guidance is
consistent in strengthening deep-layer westerlies tonight into early
Wednesday, supporting an MCS progressing east across Lower MI
overnight. While instability and buoyancy will be weaker, the
increase in shear should sustain a risk for at least strong gusts
capable of damaging winds.
...Lower Great Lakes...
Primary change is to expand category 2/Slight risk for the potential
of a few supercells this evening and a separate MCS approaching the
region near the end of the period.
Strengthening low-level warm/moist advection tied to a shortwave
impulse moving southeast from northeast to far eastern Ontario
should yield convection spreading east of the Lower Great Lakes
after 00Z. While the NAM appears overdone with the degree of
boundary-layer moistening, RAP soundings suggest convection will be
rooted from parcels around 850 mb above a nocturnal near-surface
inversion. Hodographs will be quite elongated given low-level
westerlies veering to northwesterly with height amid strong speed
shear. This setup should foster a risk for a few supercells with
severe hail probably being the primary threat centered on western NY
into northern PA. In addition, the propagation of the MCS from Lower
MI might reach the region towards 12Z with a risk for strong gusts
and locally damaging winds.
...East-central WY to the western NE Panhandle.
A front will settle south across the High Plains of interior/eastern
WY with northeasterly low-level upslope flow expected to develop by
late afternoon/early evening. Boundary-layer heating and orographic
forcing suggest a few supercells should develop along the southern
fringe of modest westerly mid-level flow. Isolated large hail should
be the primary hazard, but some severe-caliber wind gusts could
occur. This activity should spread east-southeastward toward western
NE Panhandle during the evening/late night hours.
..Grams/Moore.. 06/02/2020
$$
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