Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 020003
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
703 PM CDT Wed Apr 1 2015
.SHORT TERM: (Through Late Tonight)
Issued at 345 PM CDT Wed Apr 1 2015
MCV moving into southwest Missouri is producing an area of rain with
embedded thunderstorms. This activity is moving northeast and
should enter the CWFA around 21Z. Have therefore raised PoPs to
likely for parts of central Missouri. Not sure how far
north/northeast the rain is going to get though as some fairly dry
mid-level air as shown by AMDAR soundings from KSTL this afternoon.
However, the 850mb flow will be turning to the southwest and the
atmosphere will be moistening up...so PoPs may not be high enough
over some parts of the area this evening.
Attention turns to the cold front over the Plains and what will be
forming out there tonight. Guidance suggests that the storms will
form over Nebraska this evening and move southeast overnight.
Current thinking is that the leading edge of the precipitation will
enter the northern portion of the CWFA between 09Z and 12Z. Storms
should be on the downward trend at that point, but with MUCAPE still
potentially at or above 1000 J/kg, and around 40kts of deep layer
shear, strong storms remain a possibility across northeast Missouri
and west central Illinois before sunrise Thursday.
.LONG TERM: (Thursday through Next Wednesday)
Issued at 345 PM CDT Wed Apr 1 2015
Active cold front to move through region on Thursday. Will see
initial activity that forms ahead of front slide southeast and
diminish by 15z. Then a bit of a break before more intense round
develops during the afternoon hours. Will see MU capes approach 1500
J/kg, mainly along and south of I70 and PW values around 1.3".
Despite the cloud cover from the morning activity, any breaks in the
cloud cover will help to destabilize the atmosphere even more. Some
of the storms could be strong to severe with the main threats being
large hail and damaging winds. As for high temps, they will range
from the upper 60s far north to the low to mid 70s south.
Front to stall out over southern portions of forecast area Thursday
night and will see several waves of precipitation through Friday,
with best chances along and south of I-70. Lows Thursday night will
be in the mid 40s to upper 50s. Then colder air to filter in on
Friday as system slowly sinks south away from region. Will see non
diurnal temps, either steady or slowly falling. Highs will only be
in the low 50s far north to the low 60s far south.
Then dry weather expected for the weekend as surface ridge builds
in, with temperatures slowly moderating. Highs on Saturday will be
in the mid 50s to low 60s then warm up into the mid 60s everywhere
(Sunday night through Wednesday)
Beyond that, active pattern begins with systems sliding northeast
towards forecast area through mid week next week. Extended models
have differences in timing with these systems, so just kept chance
pops through the period. Showers and thunderstorms to move in Sunday
night and continue off and on through next Wednesday. Highs will be
in the 60s and 70s through this period.
.AVIATION: (For the 00z TAFs through 00z Thursday Evening)
Issued at 558 PM CDT Wed Apr 1 2015
Showers and a few thunderstorms ahead of an upper level disturbance
will continue in COU early this evening and eventually move into
the St Louis metro by late evening, although the activity should
begin to weaken by this time as it encounters drier air. Another
round of convection can be expected Thursday morning ahead of a
cold front which will be dropping southeastward into northwestern
MO. This activity should be gradually weakening during the morning
hours. A strong swly low level jet will lead to LLWS tonight with
s-swly winds of 40-45 kts around 1500-2000 feet in height. A third
round of convection, possibly severe is expected mainly during the
late afternoon and early evening in COU and the St Louis metro
area along the cold front as it continues to move slowly southeastward.
The surface wind will veer around to a n-nwly direction Thursday
afternoon or evening after fropa.
Specifics for KSTL: An area of showers and a few storms will move
into STL later this evening as it slowly weakens. Strong winds of
45 kts at 1500-2000 feet in height later this evening and
overnight will lead to LLWS conditions. Another round of showers
and storms can be expected Thursday morning as a weakening line of
convection drops southeastward into the area ahead of an
approaching cold front. A third round of stronger convection is
forecast late Thursday afternoon into the evening along the cold
front. This convection should weaken later Thursday evening with
lingering showers, while the surface wind veers around to a nly
direction after fropa.