Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/30/19
Area Forecast Discussion
National Weather Service Louisville KY
711 PM EDT Thu Aug 29 2019
...Updated Aviation Discussion...
.Short Term...(This evening through Friday)
Issued at 244 PM EDT Thu Aug 29 2019
Quiet, calm weather continues in the short term. Surface analysis
reveals broad anticyclonic flow around a 1021mb high centered over
northeastern Tennessee. A few diurnal cumulus have popped up across
southern Indiana and central Kentucky, otherwise skies are mostly
clear.
An MCS currently in eastern Missouri and western Illinois may send
some high level clouds our way this evening and the early part of
the overnight hours, but those should quickly dissipate. Winds will
remain light to calm, and some patchy valley fog may develop toward
sunrise. Any fog that forms should burn off quickly after sunrise.
Tomorrow will start off sunny and dry, but a cold front moving in
from the north could trigger some showers and storms across southern
Indiana during the late afternoon hours. Forecast soundings do show
some weak capping around 850mb, which should keep overall coverage
of precipitation isolated.
.Long Term...(Friday night through Thursday)
Issued at 255 PM EDT Thu Aug 29 2019
...Pleasant Holiday Weekend for Ohio Valley...
Well...on the anniversary of Katrina 2005, the medium and long term
is rather benign with temps normal to slightly above normal. A cold
front will drop into Srn Indiana and stall just north of the OH
River. Despite the GFS exuberance with 40% pops at SDF Sat-
Mon...will only have very isolated PoPS at in Srn IN counties.
However, would not be surprised to see 1-2 shra across central KY,
but confidence is low that we are not going to mention at this time.
There is very weak forcing, thin CAPE, PWATs 1.3 ish and light
winds. Any convection that does form will produce quick burst of
very heavy downpours.
Expect warm and mainly dry weather through the holiday weekend and
much of next week. A herculean high pressure ridge will amplify over
S Rockies. Looks to be a 594m ridge around the 4 Corners National
Monument. This will keep continued warm and dry conditions.
Lots of upper 80s to very low 90s for highs, but biggest change is
dew points climbing into mid upper 60s.
For Dorian... Two things to mention. One models having trouble
figuring out how strong the upper ridge will be to deflect the storm
back to the west. Lots of aircraft dropsonde data will help models.
Second, data suggests landfall (if there is FL landfall) will likely
be delayed with a slower solution.
Last tidbit...If (and when) Dorian strikes east coast of Florida,
Monday is the anniversary of the Labor Day Hurricane of 1935. It is
the strongest hurricane to ever strike the US with 200 mph winds and
26.25 inch of mercury in Florida Keys.
&&
.Aviation...(00Z TAF Issuance)
Updated at 710 PM EDT Thu Aug 29 2019
VFR conditions expected to prevail. Exceptions may be light fog at
BWG/HNB around daybreak Friday. Friday late afternoon...there`s an
outside chance for showers north of I-64, which may get close enough
to SDF/HNB, but confidence too low to include any rain chances here.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Short Term...DM
Long Term...JDG
Aviation...RJS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
631 PM CDT Thu Aug 29 2019
.SHORT TERM...
250 PM CDT
Through Friday night...
Thunderstorm coverage and severity will continue to be the
primary forecast challenge through this evening as a cold front
approaches the area.
The latest surface analysis places our cold front from near
northwestern MO, northeastward across northeastern IA and into
southwestern WI. Ahead of this front, a corridor of rich low-
level moisture, featuring 65+ degree surface dew points,
continues to work their way into northeastern IL. These dewpoints,
combined with temperatures warming into the low to mid 80s are
resulting in a corridor in which MLCAPE values are in excess of
2,000 J/KG as surface temperatures warm into the 80s this
afternoon. Meanwhile, deep layer shear continues to be elevated at
around 45+ KT thanks to some stout mid level west-northwesterly
winds.
These ingredients certainly continue to support the possibility
for strong to even severe thunderstorms over the area later this
afternoon into early this evening. However, while this is the
case, convective trends to our northwest in the vicinity of the
frontal boundary have been lackluster. For this reason, it
continues to appear that the coverage of any storms will remain
low into this evening (possible 20-30% or less). This is due to
the fact that the best upper-level support for storms will remain
to our north, so storm initiation will likely be tied to the
modest frontal boundary convergence. If any storms are able to
initiate and maintain themselves along the front, the storms
certainly could become strong enough to result in some isolated
strong wind gusts, and possible hail. With the likelihood of
lower storm coverage, I did lower POPs into the 20-30% range,
though this could still end up being too high for much of the
area.
Any thunderstorm threat should shift south of the area by mid to
late this evening as the cold front pushes across the area. The
front is expected to stall out to our south of central IL on
Friday, and this could continue to be the focus for some
thunderstorm activity on Friday. However, it appears any storm
activity on Friday will remain south of the area. Temperatures
should be cooler Friday, with highs back down into the 70s.
KJB
&&
.LONG TERM...
202 PM CDT
Saturday through Thursday...
The Labor Day holiday weekend still brings concerns for rain on
Saturday into early Sunday, though this system still remains to be
one of lower confidence. Several higher resolution models
continue to suggest a signal for less rain (or no rain at all),
but a frontal boundary will remain parked across the region on
Saturday, and moisture transport into this boundary will be on the
increase from the southwest. Global guidance such as the GFS
Ensemble and the ECMWF are still fairly aggressive with
precipitation chances, and this uncertainty unfortunately will
linger a bit longer until we can resolve where the boundary will
end up, and what moisture availability will be, especially with
convection expected to the south.
This model representation allows for everything from frequent
showers by afternoon keeping temperatures around 60 especially
north of I-80, to almost no rain at all and highs reaching near
70 in the north to 80 south. This is not all that surprising given
the nature of frontogenesis and the low amplitude wave that is
inducing it. We will continue to hold onto 40-50% chances for now
with a nod to the global guidance and the general pattern. At this
point the better chances would be afternoon or evening. Sunday
still looks like it could be quite cloudy with limited dry air
advection. While height rises will occur, weak ripples in
northwest flow With high pressure in place over the western Great
Lakes/lower Michigan will require the need for lower chances of
rain before any remnant waves depart. Either way, most of the
area will remain on the cooler side of the frontal boundary and
not in a favored area for storms.
Some moderation is expected for the first week of September as a
portion of the upper ridge to our west will nose in. After the
surface high shifts east, a more potent storm system will shift
into the upper Midwest Tuesday This will pass to our north, and
thus the thermal ridge will spread into our area ahead of the
trailing cold front. The GFS even showing some pronounced warmth
on Tuesday with metrics for near 90, though the EC remains less
aggressive (though still has mid to upper 80s based on 925mb temp
climatology). Another northwest flow cold front will skirt our
area potentially near or just after Tuesday. Lower chances for
storms will be carried both in the warm advection ahead of the low
and then with the cold front. Cooler conditions will make a re-
appearance mid week.
KMD/MTF
&&
.AVIATION...
For the 00Z TAFs...
VFR conditions expected through the period. Only significant change
to the TAF was to remove VCTS mention at ORD/MDW/GYY through 02Z
given continued decreasing confidence on any convection developing
along an approaching cold front. Recent MDW AMDAR soundings,
satellite imagery, and local sky visual all support an environment
with minimal convective chances.
The cold front is currently just west of RFD, and should clear the
Chicago metro TAFs from west to east between 02-04Z. NW winds may
remain elevated for several hours behind the front before lighter
NNW winds settle in through Friday morning. A lake breeze is then
expected to drift into ORD/MDW Friday afternoon, with medium
confidence of occurrence at ORD and medium-high confidence of
occurrence at MDW.
Kluber
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...nearshore waters
until 9 PM Thursday.
&&
$$
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Area Forecast Discussion
National Weather Service Phoenix AZ
456 PM MST Thu Aug 29 2019
.UPDATE...
Updated Aviation section.
.SYNOPSIS...
Thunderstorm activity will mainly be confined to eastern Arizona the
next few days. Meanwhile, a warming trend is expected through
Saturday as the Monsoon High migrates into northern Arizona. High
pressure will continue to slide towards the Four Corners Sunday,
resulting in an easterly flow and a more favorable setup for
increasing moisture and thunderstorm activity.
&&
.DISCUSSION...
Temperatures this afternoon across south-central Arizona have been
struggling, which is a reflection of the atmospheric overturning
that occurred from the rainfall last evening. Latest ACARS soundings
indicate that the relatively cool air extends through about 750 mb,
which is producing poor lapse rates and significant convective
inhibition.
Suite of hi-res guidance including the HREF is in very good
agreement, suggesting afternoon convection will be limited to the
mountainous areas of eastern Arizona. Northwesterly steering flow
around the anticyclone centered across the northern Baja peninsula
will also hinder propagation into the lower deserts. Forecast PoPs
are above the National Blend, but generally less than 5 percent in
the Phoenix area.
The aforementioned anticyclone will drift northward Friday,
producing a relatively dry northwesterly flow with weak NVA across
much of Arizona. Consequently, convection will again be
confined to the higher terrain of Gila County. Meanwhile, thickness
increases will again boost temperatures towards the 110 degree mark
in the lower deserts, and an Excessive Heat Warning remains in
effect for Friday (and Saturday).
&&
.PREVIOUS DISCUSSION...
The H5 high will continue its migration towards the Four Corners
area through the beginning of next week. This will allow for deeper
easterly flow capable of bringing richer moisture into Phoenix
and west past the Colorado River and into southeast California.
Upper air support for convection may also improve with multiple
inverted troughs circulating through southern Arizona.
Consequently, PoPs increase slightly Sunday through Wednesday but
isolating which day is the most favorable for storms is not clear.
&&
.AVIATION...Updated at 2356 UTC.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Convective activity that is currently over the higher terrain well
north and east of the Phoenix area is still not expected to make it
into the lower elevations this evening. However, latest high-res
models do indicate risk of a weak outflow making its way into the
north valley, switching winds to northerly for a couple of hours at
KSDL and possibly KDVT, but not making it all the way to KPHX or
KIWA. Westerly winds are expected to switch to more typical easterly
drainage winds late this evening/around midnight. CIGS to be limited
to FEW-SCT mid/high layers through the night. Easterly winds to
switch a little earlier to westerly on Friday with convective
activity once again remaining well north and east of the terminals.
Southeast California/Southwest Arizona including KIPL and KBLH:
Expect clear skies with familiar diurnal winds patterns favoring
south and southeast directions and occasional gustiness.
Aviation Discussion not updated for amended TAFs.
&&
.FIRE WEATHER...
Sunday through Thursday:
The Monsoon High will migrate towards the Four Corners early next
week and ultimately into the southern Plains. This will result in an
easterly flow, which will be favorable for increasing relative
humidities and at least isolated storms each day, particularly
across eastern Arizona. A cooling trend is anticipated through the
middle of next week, though temperatures will remain at or above
normal.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM Friday to 8 PM MST Saturday
for AZZ530>532-534-536>538-540>546-548>551-553>556-559-560-
562.
CA...Excessive Heat Warning from 10 AM Friday to 8 PM PDT Saturday
for CAZ563-566-567-569-570.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Deems
AVIATION...Percha/AJ
FIRE WEATHER...Hirsch