Area Forecast Discussion
Issued by NWS Paducah, KY
FXUS63 KPAH 230837
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
337 AM CDT Sat Aug 23 2014
.Short Term /Today through Monday/...
Issued at 335 AM CDT Sat Aug 23 2014
The primary concern in the short term continues to be heat indices.
Little or no change will be made to peak forecast heat index
values...which should be similar to Friday /100 to 108 degrees/.
Although high temperatures will be lowered slightly...dew points
will be raised slightly. Through Monday...peak heat index values
should continue to range from around 100 in southwest Indiana to
around 105 in southeast Missouri.
A secondary concern is convective potential...which the models have
shown little skill at predicting. Overall...convective potential
appears a little higher than previous forecast packages indicated.
Slight chance pops will be expanded westward to the Mississippi
River today and tonight. The highest potential today through Monday
still appears to be in southwest Indiana and the Pennyrile region of
western Kentucky. Those areas will remain on the eastern periphery
of the mid level ridge axis through Monday. Will carry slight chance
pops in those areas virtually every period through the short term.
A small mesoscale convective system was sinking southward across the
Pennyrile region of western Kentucky early this morning. This mcs
appears to be related to a subtle 500 mb impulse rounding the top of
the mid level ridge. Additionally...a weak surface
trough/convergence zone was located from central Illinois southeast
across southwest Indiana. The models missed the impulse...but they
have done well with the surface trough. The trough is forecast to
sag southwest to the Mississippi River by this evening. This is the
basis for expanding slight chance pops westward to the Mississippi
River today into tonight. The models wash out the trough late
tonight...leaving a diffuse pressure gradient and a broad area of
light southeast to south winds Sunday through Monday.
As stated above...forecast highs will be lowered slightly. 850 mb
temps are not forecast to climb any higher than previous days. Mos
guidance highs for today through Monday have fallen just a bit
/especially nam mos/...and mos highs have generally been verifying a
little too warm on recent days. However...dew points have been a
little higher than forecast...with no mixing down of drier air in
the afternoons. The higher forecast dew points will offset the lower
temps...leaving the heat index forecast unchanged.
.LONG TERM / Monday Night through Friday Night /...
The 00Z GFS, GEM, and ECMWF cool low-level temperatures by a few
degrees Tuesday in comparison to Monday. It appears that they all
take winds to the east or southeast Monday night which results in
some cooling. Not sure how much to trust such a subtle change, but
with dewpoints holding in the low to mid 70s, heat indices will
still flirt with triple digits. so the heat advisory will remain in
effect through Tuesday.
The 00Z models also continue to generate a smattering of QPF in the
heat of the day Tuesday and Wednesday. See little reason to not keep
slight chances each day. It appears that temperatures should still
reach at least the lower 90s Wednesday.
The GFS diverges from the ECMWF and GEM with the upper pattern
Thursday and Friday. The GFS really builds the ridge in the west,
which pushes the northwest U.S. upper trough progressively eastward,
reaching the western Great Lakes by Thursday morning. This pushes a
cold front and band of convection eastward through our area
Wednesday night and Thursday. This leads to a dry and cool end of
the work week.
The GEM and ECMWF are more subdued with the western ridge and keep
the westerlies nearly zonal along the Canadian border. This pushes
the western trough into the Plains by Thursday and results in a
weaker system that does not reach the area until next weekend.
Really don`t have a good feel on which of these ideas to follow. If
the ECMWF is correct, would not be surprised to see a continuation
of the hot and humid conditions through next work week. For now will
lean toward the GFS and show a weak frontal passage on Thursday with
a nice cool down to slightly below normal levels by Friday. Will
keep 20-30% PoPs from Wednesday night through Friday just to
cover all the bases until things come into better focus.
Issued at 1145 PM CDT FRI AUG 22 2014
Convection moved into the KEVV/KOWB sites a bit earlier then
expected but mainly impacted the KOWB terminal. This activity should
continue to move south and out of the area soon with not much
organized convection expected for the rest of the night. The area
will be under high pressure aloft on Saturday but a very weak
frontal boundary or trough will be bisecting the area, and may be
enough to spark isolated to sct convection during the day
areawide. Opted to add a vcts to all sites to highlight this
potential. Otherwise, light winds and some cu will likely develop.
KY...HEAT ADVISORY until 7 PM CDT Tuesday FOR KYZ001>022.
MO...HEAT ADVISORY until 7 PM CDT Tuesday FOR MOZ076-086-087-100-
IL...HEAT ADVISORY until 7 PM CDT Tuesday FOR ILZ075>078-080>094.
IN...HEAT ADVISORY until 7 PM CDT Tuesday FOR INZ081-082-085>088.