Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/03/23
Area Forecast Discussion
National Weather Service La Crosse WI
1037 PM CDT Sat Sep 2 2023
.DISCUSSION...(This evening through Saturday)
Issued at 250 PM CDT Sat Sep 2 2023
Key Messages:
- A hot holiday weekend continues with heat indices in the
mid-90s to around 100 degrees through Tuesday.
- Critical fire weather concerns for southwest Wisconsin Sunday
afternoon owing to the unseasonably warm temperatures combined
with low humidity values, gusty winds, and dry fuels from the
ongoing drought. See the dedicated fire weather discussion
below for more details.
- Only notable chance of showers and storms comes Tuesday evening
into Wednesday with seasonal weather for the middle to end of
the week.
Heat Details through Tuesday
Upper level ridging is well established across the central CONUS
early this afternoon with the region under its northern periphery.
A corridor of mid-level frontogenetical forcing across central
Wisconsin coupled with a passing upper tropospheric wave over the
northern Great Lakes led to a band of showers and thunderstorms
north of Interstate 94 this morning, with shower intensity and
coverage waning as the wave pushes off to the east this afternoon.
To the south of this corridor, mostly clear skies dominated
during the day with highs in the lower to mid-90s.
The thermal ridge builds in for Sunday as lower tropospheric
temperatures in the warm nose push +28 to +30 degrees C. A fetch
of drier air off the southern and central High Plains, coupled
with waning evapotranspiration owing both to seasonal changes and
the ongoing drought will keep dew points in the mid to upper 50s
during the afternoon on Sunday. HRRR forecast soundings show deep
and efficient mixing up to 800-700-mb, which should result in high
temperatures in the upper 90s to around 100. Confidence in this
forecast is high, though expect that there will be some spatial
variability in temperatures beyond the forecast owing to the drier
nature of the airmass.
The thermal ridge retrogrades to the north and west on Monday as
the upstream pattern amplifies, but the overall differences
between Sunday and Monday will be minimal from a temperature
standpoint. Finally, for Tuesday, what had been a quasi-stationary
lee trough over the Dakotas begins to slide eastward in response
to a sharp shortwave trough ejecting from the central Rockies. The
lower tropospheric flow turns more southerly ahead of this
boundary/shortwave and brings Gulf moisture back northward for the
day on Tuesday. Thus, while high temperatures will be lower
compared to the last 3 days, heat indices may actually be very
similar with dew points forecast to be 10 degrees higher.
All put together, did go ahead with an extended heat advisory
through Tuesday down the Mississippi River Valley to the
Wisconsin River given the prolonged nature of the unseasonable
heat. Heat indices on any given day will only flirt with the
traditional advisory criteria of 100-105 degrees F. However,
there exists a stipulation that 4+ days with heat indices of
95-99 degrees F is sufficient for an advisory--which is met down
the Mississippi River Valley when factoring in today`s heat
indices.
Next Round of Showers and Storms on Tue/Wed
The frontal boundary slides steadily southeastward through the
evening on Tuesday evening through Wednesday morning as the mean
trough (with several embedded vort lobes) carves out the northern
side of the Southern Plains ridge. There exists some spread in the
guidance with respect to the timing of the front, but nothing too
outlandish for this range out. This will be the only real shot of
showers and storms for the week with split flow reigning for the
remainder of the week, though the one consolation with this late
week pattern is that temperatures should hold to near normal for
this time of year (highs in the upper 70s to low 80s).
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 1037 PM CDT Sat Sep 2 2023
VFR conditions will prevail at both RST/LSE taf sites through the
taf period. Wind speeds have diminish slightly across the area...near
10 knots at both taf sites. With stronger winds aloft...low level
wind shear is expected to develop at both taf sites. Have
continue to mention low level wind shear in the tafs tonight into
Sunday morning. Started low level wind shear at the beginning of
the taf period. Due to daytime heating during the day
Sunday...winds are expected to mix down aloft and be sustained at
10 to 15 knots with gusts to around 25 knots.
&&
.FIRE WEATHER...
Issued at 250 PM CDT Sat Sep 2 2023
Sunday continues to be the day of the highest fire weather
concerns for southwestern into central Wisconsin. Afternoon
forecast soundings show the potential for enhanced mixing given a
20-30 C dewpoint depression at 5-8 kft AGL which may result in
lower humidity values than currently forecast. While the going
forecast has afternoon dewpoints falling into the mid-50s, there
is a 30% chance that localized, deeper mixing pushes these values
closer to 50 degrees and RH values down to around 20%, especially
in sandy regions of southwestern Wisconsin and in valleys that see
higher temperatures. The stressed and dry vegetation owing to the
ongoing drought further adds to the threat with build-up indices
exceeding 100 across southwest Wisconsin on Sunday afternoon.
Have issued a Fire Weather Watch in collaboration with the WI DNR
to address this threat. The wind component of the forecast is a
bit more borderline for the issuance of a Red Flag Warning, with
sustained values of 15 mph right on the threshold for needing a
warning. These values taper off the further north one travels
through Trempealeau and Jackson counties, where confidence in
reaching warning-level winds is the highest in the southern parts
of these counties.
The risk for at least elevated fire weather conditions continues
through Monday, with the risk decreasing for Tuesday as higher
dewpoints arrive. The next chance of wetting rains does not arrive
until Tuesday night into Wednesday morning as a cold front moves
in.
&&
.CLIMATE...
Issued at 250 PM CDT Sat Sep 2 2023
Near record to record temperatures are forecast for Sunday and
Monday.
Sunday, September 3 Record High Forecast
-----------------------------------------------
La Crosse 95 set in 1929 100
Rochester 94 set in 1937 96
Monday, September 4 Record High Forecast
-----------------------------------------------
La Crosse 95 set in 1925 98
Rochester 95 set in 1893 95
Maximum Temperature Record for September
-----------------------------------------------
La Crosse 101 set on Sep 6, 1922
Rochester 100 set on Sep 6, 1913
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Heat Advisory until 6 PM CDT Tuesday for WIZ032-033-041-053-054.
Fire Weather Watch from Sunday afternoon through Sunday evening
for WIZ033-034-041>044-053>055-061.
MN...Heat Advisory until 6 PM CDT Tuesday for MNZ079-088-096.
IA...Heat Advisory until 6 PM CDT Tuesday for IAZ011.
&&
$$
DISCUSSION...Skow
AVIATION...DTJ
FIRE WEATHER...Skow
CLIMATE...KAA/Skow
Area Forecast Discussion
National Weather Service Melbourne FL
811 PM EDT Sat Sep 2 2023
.DISCUSSION...
...Dangerous Surf, Including Numerous Life-threatening Rip
Currents, Expected Through the Holiday Weekend...
...Hazardous Boating Conditions, Especially in the Gulf Stream...
Current-Overnight...Drier PWATs pushing westward across the coastal
waters and eastern FL peninsula this evening, with this trend
continuing westward overnight. Local HRRR suggests weak coastal
troughing which could allow for a few (20pct) low-topped coastal
showers to develop and creep onshore late into early Sun morning.
NNE-NE-E onshore surface flow will become light and expect PCloudy
skies, but could see small periods of BKN stratocu along the coast.
Slightly cooler overnight mins forecast with L-M70s, except U70s
along the immediate coast and adjacent barrier islands.
Dangerous conditions in the surf zone are occurring with numerous,
strong life-threatening rip currents present due to a persistent
long period swell, in addition to rough/choppy surf and large
breaking waves. Entering the surf is strongly discouraged.
Sunday-Labor Day...Previous Modified Discussion...Mid/upper level
high pressure will dominate the region, with surface high pressure
building across the SE US. Locally this will allow the NE surface
flow to remain in place, with drier air continuing to filter across
the area limiting rain chances through the period. Have a token 20
pct chance of rain across ECFL as onshore flow should be deep enough
for a few onshore-moving showers, and the only mentionable higher
chances (PoP 20-30 percent) will occur along the coast, confined
from southern Brevard to Okeechobee County south/east. Expect plenty
of sunshine with less humid conditions through the period. While
temperatures will be at or just below seasonable values, it will
still remain very warm. Afternoon highs in the mid to upper 80s on
Sunday, and upper 80s to near 90 degrees on Monday. Overnight lows
will be in the low to mid 70s.
Swell from Post Tropical Cyclone Idalia will continue to be the main
weather concern through the holiday weekend. This will produce
rough/choppy surf and a high risk of life-threatening rip currents.
Entering the surf is not advised.
&&
.MARINE...Overnight-Sun Night...Onshore flow remains
stout/persistent near 15 kts. The pressure gradient does relax
slightly late Sun-Sun night. Seas continue higher than model
forecast in mostly swell, thanks in part to Idalia, 4-6 ft very near
shore and 6-9 ft offshore/Gulf Stream. Boating conditions remain
hazardous and a Small Craft Advisory (SCA) remains in place for all
marine legs. An extension of the current SCA configuration may be
needed for the Gulf Stream Sun night. The next forecast shift can
take another look as we may be able to back off the SCA for near
shore Volusia in favor of Exercise Caution on Sun - as seas are
currently forecast 5-6 ft here. Isolated, low-topped, showers also
in the forecast.
&&
.AVIATION...Mainly VFR conditions continuing. Light onshore flow
tonight, with a slightly tighter pgrad on Sun as NE/ENE winds
increase in upwards of 10-15 kts and higher gusts, especially late
morning and afternoon. Convective chances below average with drier
air in place. Some low-topped coastal showers possible as highest
(20-30pct) rain chances will lie across the coastal TAF sites.
&&
.MLB WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...Small Craft Advisory until 8 PM EDT Sunday for AMZ550-552-555-
570-572-575.
&&
$$
Sedlock/Heil