Scientific Forecaster Discussion
fxus63 karx 190853
Area forecast discussion
National Weather Service La Crosse WI
353 am CDT Fri Jul 19 2019
issued at 348 am CDT Fri Jul 19 2019
Decided to expand excessive heat warning to include all but Taylor
County in north central Wisconsin. Taylor County is now in a heat
advisory today. See latest npw product or watches, warning,
advisory section at bottom for details.
Short term...(today through Saturday night)
issued at 256 am CDT Fri Jul 19 2019
Currently watching ongoing problematic heavy rain producing
thunderstorms lined up mainly along the I-90 corridor and just
south. Cams show this convection eventually moving east of the area
by 7-8am as the low level jet bends further east and tapers.
Attention then turns to heat today and then enhanced severe threat
late this afternoon into tonight. A warm front will be lined up
approximately between the I-90/94 corridors. Rap showing 925mb
temperatures increasing into the 29-31c range by this afternoon with
partly to mostly sunny skies. This is expected to translate to highs
well into the 90s across much of the area along with uncomfortable
dewpoints in the 70s. Resulting heat indices will generally be in
the 100-105 range north of I-90, and 105-110 across portions of
northeast Iowa/far southwest WI. Will leave heat headlines alone as
they cover this well.
High heat and humidity (cape of 5000+ kj/kg) + warm frontal boundary
+ ample bulk shear (35-50kt) will lead to an enhanced risk of severe
thunderstorms by this evening into the overnight hours. All severe
threats (damaging winds, large hail, tornadoes) will potentially be
experienced as well as a flash flood risk if storms train over the
same area. The highest severe threat looks to be north of the I-90
corridor where that warm front will be hanging out. Will be
monitoring this situation closely!
Likelihood of thunderstorm continue into Saturday/Saturday night as a
mid-level trough crossing the northern plains begins to drive a
surface cold frontal boundary southward into the area. Will again
have to be situationally aware of severe/flash flooding threat as
there will still be plenty of cape and shear to work with.
Long term...(sunday through thursday)
issued at 256 am CDT Fri Jul 19 2019
Could still be a chance of shower/thunderstorms south of I-90 Sunday
morning as that cold frontal boundary sags slowly southward out of
the area. Otherwise, cooler/drier air filtering into the area as
Canadian high pressure builds into the region. Quiet/cooler weather
continues through Thursday as the Canadian high settles over the
Aviation...for the 06z tafs through 06z Friday night)
issued at 100 am CDT Fri Jul 19 2019
Cigs: generally expecting VFR through the period, with more of a
scattering out toward morning on Friday. That said, a few models
suggest that MVFR cigs will develop mostly Post the current
convection - and some hints of this. For now will hold mostly VFR
and adjust if needed.
Weather/vsby: west-east running frontal boundary continues to serve as a
focus for shra/ts development with low level jet impinging/fueling
it. As the jet noses into southeast WI overnight, so should the
pcpn. Expect most to shift east/southeast of the taf sites by 09z.
Could see another round of shra/ts overnight Friday night as the
current boundary pushes north on Friday, but then takes a turn back
south as a shortwave upper level trough tracks east across northern
portions of the region. Better chances could hold off until after
Winds: mostly south and on the lighter side. Should increase for
Friday afternoon as sfc pressure gradient starts to tighten.
WI...excessive heat warning until 7 PM CDT Saturday for wiz054-061.
Excessive heat warning until 7 PM CDT this evening for wiz029-
Heat advisory from 1 PM this afternoon to 7 PM CDT this evening
Minnesota...excessive heat warning until 7 PM CDT this evening for mnz079-
Iowa...excessive heat warning until 7 PM CDT Saturday for iaz011-018-
Excessive heat warning until 7 PM CDT this evening for