Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/01/19
Area Forecast Discussion
National Weather Service Des Moines IA
858 PM CDT Mon Sep 30 2019
.UPDATE...
Issued at 858 PM CDT Mon Sep 30 2019
Forecast on track with rapid expansion of storms over Nebraska in
ribbon of strengthening H850 low level jet and weak height falls
suggesting first wave rippling northeast into KS/NE/MO now.
Incredibly anomalous H850 moisture continues to funnel north into
Iowa with H850 dew points of 15 to 17C continuing to be advected
our way. Have continued FFA over same locations with recent update
at 842 pm. PWATs continue to be forecast to 2 to 2.35 inches by
18 to 00z over the region Tuesday into Tuesday evening. This
combined with warm cloud depths of 4 to 4.5km (12kft to 14kft)
will yield very efficient rainfall processes. Added some wording
to the FFA to include potential to affect traffic flow/speed and
generally poor travel conditions during morning/afternoon commutes
in bands or areas of heavy rainfall. Main wave still expected to
arrive late tomorrow and tomorrow night which will bring the more
widespread heavy rainfall to the region. /rev
&&
.DISCUSSION.../Tonight through Monday/
Issued at 354 PM CDT Mon Sep 30 2019
The primary concern today remains significant convective trends
overnight through Tuesday Night with heavy rains and at least
some flooding likely. There is also an increasing severe weather
potential southeast half late Tuesday, which is a change from
recent runs. Secondary concerns also include low confidence frost
potential north Thu Night north with below normal temperatures to
end the week.
Initially this afternoon Iowa is well into the warm sector with
warm, humid conditions in brisk SSW winds. MLCAPEs are 1500-2500
j/kg but with little convergence or baroclinicity, and only small,
minor CINH erosion along the approaching cold front in the
Siouxland area, there will not likely be much development until
the late evening hours. Water vapor imagery does not show much at
the moment, but most models suggest QG forcing will overspread the
Siouxland area by midnight aided by 850/700mb frontogenesis along
and just behind the front. MUCAPEs will stay around 1500 j/kg,
but with little effective shear the severe potential will be
minimal. Heavy rains and flooding will be the primary threat. It
would be difficult to produce a better environment in these
regards with daily climatological record specific humidities and
precipitable waters suggested by both recent EC ensemble and NAEFS
runs, which would be atypical anytime of year. Compounding the
concern will be the slow moving frontal boundary with mean winds
parallel to the front suggesting training, and a steady fetch of
strong, deep moisture transport. The 305K isent surface near the
effective inflow base notes little baroclinicity, but a steady
stream of 30-40kts of flow above the lower level frontal
convergence with consistent trajectories from the Rio Grande
Valley and TX tonight through Tue Night. Although not uniform
across the entire forecast area due to the nature of convection,
many locations may see one to three inch rainfall totals by early
Wednesday with locally higher amounts expected. The HRW ARW run
this morning suggests isolated max amounts may reach five to six
inches with similar suggestions from the 12z HREF Local
Probability Matched Mean somewhere across west central over
northern Iowa.
The severe potential cannot be overlooked southeast Tue afternoon
and evening as well with those locations still in the warm sector
and the long wave trough progression eventually increasing deep
shear south and east of the frontal boundary, unlike expectations
for this evening. This could result in supercells with recent HRRR
and 4km NAM guidance suggesting that as well with enhanced
updraft helicity tracks through central IA. There is not much
backing ahead of the front, which may keep the low level shear,
SRH and tornado threat down somewhat, but if a potent cell can
track near the front a tornado is certainly not out of the
question in a very locally enhanced near storm environment. LCLs
should be quite low too.
The front and heavy rain potential should be relegated to the
IA/MO border Wed, but one recent model change has been a trend
toward stronger forcing associated with long wave trough passage
at this time. This has resulted in stronger synoptic lift and higher
PoPs lingering longer into Wed with a stronger surface reflection
now very briefly bringing the warm sector back into southeast IA.
This may result in another burst of heavy rains for those
locations late Wed before cooler, drier conditions are in place to
end the work week.
Strong subsidence should be in place Thursday with the attention
turning toward frost potential Thursday Night as surface high
pressure settles into the area. Favorable items for frost will be
light winds and clear skies, but surface temps only dip into the
upper 30s with dewpoints similar or only a few degrees below.
Obviously decent uncertainty at this time range, but the low level
moisture may be too high for vegetation temps to dip sufficiently
resulting in a cold dew or fog rather than frost. Something to
continue monitoring however.
The next precip window appears to be around Saturday with
deterministic and ensemble solutions in better agreement with mass
fields and timing. This results in showers likely, and possibly a
rumble of thunder, but overall return flow will not be sufficient
for instability or severe potential. The depth and strength of
the phased thermodynamic and kinematic forcing may still be
sufficient for a short period of moderate rainfall however. After
this, dry conditions and continued below normal temperatures are
anticipated with fairly good model agreement for this time range
with surface high pressure behind the passage of the long wave
trough.
&&
.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 641 PM CDT Mon Sep 30 2019
Convection expected mainly northwest of area through 06z, then
shra or VCTS working south and increasing in coverage through 12z
north sites KFOD, KMCW, and KALO. Cigs will drop from VFR to MVFR
between 08-12z north sites then further drop to IFR aft 12z over
the same above sites. South site KOTM will remain VFR through
entire period while KDSM expected to drop to mix of MVFR/VFR from
13z through end of period. Thunder risk again increases over most
of area aft 12z with periods rain and sct thunder north
sites...while KDSM more sct thunder. Heavy rain/lower vsby
expected as well during period. Timing of worst conditions will
need some adjustments through end of forecast aft 12z. /rev
&&
.HYDROLOGY...
Issued at 354 PM CDT Mon Sep 30 2019
Most models suggest conditions and forcing will be optimized Tue
and/or Tue Night for the best heavy rain/flooding potential
rather than overnight tonight so have expanded the Flash Flood
Watch farther south and east to increase the likelihood of
capturing heavy rains, and also better antecedent soil conditions
south where recent heavy rains have fallen.
Preliminary RFC river forecasts, based on 72 hours of QPF from the
12z forecast cycle, have resulted in specific River Flood Watches
for minor flooding being issued for several locations in the
Cedar, Des Moines and Raccoon River basins. Confidence in these
river forecasts is low to medium however due to the extended range
of forecast rainfall, and difficulty of pinning down the
magnitude and locations of what can be very localized heavy
rainfall maximums. Within bank rises and moderate flooding are
still within the realm of possibility.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 7 AM CDT Tuesday through Wednesday
morning for IAZ027-028-038-039-049-050-060-061-072>074-082>084-
093>095.
Flash Flood Watch through Wednesday morning for IAZ004>007-
015>017-023>026-033>037-044>048-057>059-070-071-081-092.
&&
$$
UPDATE...REV
DISCUSSION...Small
AVIATION...REV
HYDROLOGY...Small
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
845 PM CDT Mon Sep 30 2019
.UPDATE...
Updated for evening discussion.
&&
.DISCUSSION...
Another warmer than normal night can be expected with clear skies
and lows near or at 70 degrees area wide. A few patches of ground
fog is possible in the early morning for areas in the southeast.
No major changes were made to the forecast./JNE/
Prior discussion below:
Tonight and Tuesday: a persistence forecast with dry weather and
record afternoon temperatures are expected again Tuesday. Mid
afternoon satellite imagery and RAP analysis showed very suppressed
cumulus clouds beneath a large 595dam high centered over northern
Mississippi. Mid afternoon surface analysis had an >1018mb ridge
nosing into our CWA from the northeast. These features will change
little through Tuesday. Temperatures this afternoon were climbing
into the mid 90s and are set to top out in the mid to upper 90s.
This will tie and set new record highs at a few locations.
Temperatures will top out in the mid to upper 90s again Tuesday. The
sites at greatest risk of setting record highs Tuesday include
Greenville, Greenwood, Vicksburg and Meridian. Tonight will be
similar to the last few nights with mostly clear skies and a near
calm winds with low in the upper 60s to lower 70s. Patchy light fog
development will be possible in the south along the Highway 84
corridor but dense fog is not currently anticipated. /22/
Tuesday night through Thursday night...Strong high pressure at the
surface and aloft will continue on Tuesday night into Wednesday,
with lows falling into the lows 70s. The upper ridge will keep
its grip over the region on Wednesday, with highs climbing into
the mid/upper 90s once again. The ridge will weaken over the
region on Thursday, out ahead of a cold front that will move into
north Mississippi Thursday evening. The front will continue to
move south across the area Thursday night into Friday, ushering in
a drier airmass and slightly cooler temperatures. Highs on Friday
will range from the mid 80s in the north to low 90s in the south.
The main concern on Friday will be increasing fire weather
conditions, with a combination of breezy winds and min Rh`s
falling into the 30 percent range. This will have to be monitored
for possible inclusion in the HWO/Graphicasts through the week.
Saturday will continue to be dry, but the winds will decrease
across the area as the surface gradient weakens. Rh`s will fall
into the upper 20 to lower 30 percent range though, so will have
to monitor for fire weather concerns once again on Saturday. The
surface flow will swing back around to the south on Sunday and
with afternoon heating, there will be a chance for isolated
thunderstorms. All of the global models are in pretty good
agreement of a stronger cold front moving across the area Monday
or Monday night, although the models do not agree on the strength
or the amount of precip associated with the boundary. Either way
it does look like cooler and more seasonable weather will be on
tap for next week./15/
&&
.AVIATION...
00Z TAF discussion:
VFR conditions and light wind will prevail through the forecast
period, but an expection is the potential for IFR/LIFR early
morning fog in the HBG/PIB area given the persistent weather
pattern. /EC/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 69 96 72 96 / 0 0 0 1
Meridian 69 97 71 97 / 0 0 0 1
Vicksburg 69 97 72 97 / 0 0 0 1
Hattiesburg 68 95 71 94 / 0 2 0 2
Natchez 69 94 71 95 / 0 0 0 1
Greenville 69 97 72 97 / 0 0 0 0
Greenwood 70 96 72 96 / 0 0 0 0
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.
&&
$$
JNE
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
342 PM CDT Mon Sep 30 2019
.SHORT TERM...(This evening through Tuesday night)
Issued at 338 PM CDT Mon Sep 30 2019
Main concerns this period are conditional severe weather threat
this evening, and the heavy rainfall threat for tomorrow
clipping our far south along I-90 (with Iowa, extreme SE MN, and
Wisconsin more in the heart of the threat).
As of this afternoon, the surface low was centered just west of
Alexandria, with the warm front draped east across central MN.
Temperatures south of the front have risen into the 80s with dew
points commonly in the low 70s. Over 3,000 J/kg of CAPE is present
in the warm sector, and hi-res guidance indicates some broken
convection developing after 22Z along the approaching cold front
which is now approaching the MN border from the Dakotas. The main
question is the temperatures aloft, with +12C noted at 700mb based
on RAP analysis. This warm air aloft reduces confidence in
widespread convection, and explains why pops were limited to the
40- 50% range along the line. There will likely be thunderstorms,
but just how widespread they will be is somewhat uncertain and
dependent on overcoming the CAP. For storms that do initiate,
supercells are possible given 40 knots of effective shear and
ample instability. Large hail, damaging wind, and a few tornadoes
could occur if storms become surface based, especially near the
low/warm front.
The cold front will move through our area overnight, cooling
temperatures by nearly 30 degrees by morning. The frontal zone
then becomes nearly stationary by tomorrow, oriented from Iowa
toward northern WI. This will be the focus of additional shower
and thunderstorm development through the day tomorrow and tomorrow
night, which will likely be a long duration rainfall event for
far southern MN. On the north side of the front, instability will
be present, but weak. PWATs will remain high, and lapse rates
modest at best. So, heavy rain is the primary threat with the
severe threat shunted south of the frontal boundary. Could foresee
2-3" of rainfall or isolated higher amounts along I-90 and in
collaboration with the Des Moines and La Crosse NWS offices, have
issues a Flash Flood Watch for tomorrow and tomorrow night for
along I-90 to the east of Fairmont.
.LONG TERM...(Wednesday through Monday)
Issued at 338 PM CDT Mon Sep 30 2019
The period will commence with an elongated E-W surface front
stalled from the Central Plains through the northern Ohio Valley.
Widespread rainfall will be ongoing in the vicinity of the front,
mainly for southern MN into southwestern WI, where low level
convergence and high moisture depth will be concentrated. While a
few thunderstorms are possible, the main hazard will be heavy
rain.
This activity will gradually wane Wednesday night into Thursday as
the front finally gets impetus to shift off to the southeast due
to incoming modified western Canadian high pressure. This will
produce a break from precipitation Thursday night through Friday
evening. The main concern will be when the center of high pressure
is directly overhead, allowing for clear skies and light winds,
and this is expected early Friday morning. With the cold air
advection expected into the area behind the departing cold front
and with the incoming high pressure, temperatures for central MN
will fall to the mid-30s which would be conducive to an early
October frost.
The next significant frontal system gets its start over MT/WY on
Friday then progresses east across the Dakotas Saturday and moves
into the Great Lakes on Sunday followed by high pressure once
again early next week. This system will be the next rain-maker
for the area, with the potential for some rain amounts in the
0.25-0.50" range for next weekend.
As for temperatures, today`s one-day jump to summer-like
temperatures, highs will drop to the mid 50s to mid 60s on
Tuesday behind the front. Modest cold air advection will continue
into late week, keeping highs in the low 50s to low 60s while lows
generally remain in the mid 30s to upper 40s.
&&
.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1239 PM CDT Mon Sep 30 2019
Warm front slowly lifting through the area today, with the surface
low along the western MN border, moving NNE with time. Winds have
turned SSW south of the front, and gusts over 20 knots can be
expected to continue through the afternoon. Along and north of the
front, plenty of low stratus is in place along with easterly
winds. Some cu developed south of the front but should be mainly
VFR through the afternoon. As the low lifts into northern MN this
evening, the cold front will move west to east across the local
area, with a chance for thunderstorms to develop along the front
from about 22-03Z this evening. Coverage remains a big question
mark with this setup, so continued to opt for VCSH wording in the
TAF as confidence is too low at this time to commit to VCTS.
KMSP...Thunderstorms are possible late afternoon-evening, but
confidence too low to include VCTS at this time due to coverage
being uncertain.
/OUTLOOK FOR KMSP/
Wed...VFR/MVFR. Chance -RA. Wind NE 5-10 kts.
Thu...VFR. Wind NW 5-10 kts.
Fri...VFR. Wind SSE 5-10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Flash Flood Watch from Tuesday morning through Wednesday morning
for MNZ085-092-093.
&&
$$
SHORT TERM...SPD
LONG TERM...JPC
AVIATION...SPD