Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Jackson MS
908 PM CDT Tuesday Sep 16 2014
Update...a training complex of thunderstorms over the Hattiesburg
area has made for a busier than anticipated evening at the office.
Almost 3 1/2 inches of rain has been measured at the hbg ASOS so
far...and dual pol estimates suggest over 4 1/2 inches may have
fallen in the city of Petal. Just a few miles north in areas of
southern Jones County...no rain has fallen. Such is summertime
weather in the arklamiss. This activity...and additional convection
extending along the MS/la border has been ongoing along a lingering
surface trough. Though there isn't much of a surface moisture
gradient with this feature...there is a gradient in atmospheric
moisture content...with the 00z kjan precipitable water at 1.65 inches increasing
to 2 inch precipitable waters indicated closer to the coast. There were also
respectable 0-6 km bulk shear magnitudes in the 20-30 knots range
helping to maintain this convection. However with the loss of
daytime heating...there should be a gradual decrease in activity
over the next few hours. The forecast was updated to keep in probability of precipitation
for another couple hours across the far south and to adjust hourly
temperatures/dewpoints based on current trends. For the remainder of the
area...no major adjustments were needed. /Dl/
Aviation...VFR conditions prevail across all taf sites this
evening...except at hbg where showers and thunderstorms persist.
Here brief IFR conditions will continue to be possible through 930
PM. After that time scattered showers and storms in southeast MS should be
dissipating. In hbg (and perhaps near pib) IFR to potentially LIFR
flight cats will be possible late tonight through 9 am tomorrow due
to a combination of low clouds and fog. Elsewhere VFR conditions
will continue overnight tonight...but some MVFR visibilities due to
patchy fog can't be ruled out early Wednesday morning. For tomorrow
anticipate relatively light north surface winds with isolated to
scattered afternoon showers and storms confined mainly to pib/hbg.
Discussion... /issued at 250 PM CDT Tuesday Sep 16 2014/
short term...through Thursday night...the surface high will shift
east and weaken into Wednesday. Although the shortwave will shift
east as well...ridging aloft will amplify in the west while upper
level troughing deepens in the east resulting in a northwest flow
aloft over our County Warning Area. This will help the cold front drift south of our
County Warning Area by Wednesday morning and then stall near the Gulf Coast.
Slightly cooler and drier air is expected over our County Warning Area Wednesday.
The 12z Tuesday Jan sounding showed a precipitable water of 1.95inches. By 12z Wednesday
precipitable waters are expected to be around an inch and a third. Surface dew
points will drop in the 60s overnight allowing most sites to bottom
out in the middle 60s Wednesday morning. Normal lows for this time of
the year run 63-66f.
Northwest flow aloft will continue over our region through Thursday
night and models agree that a couple of subtle shortwaves will set
off convection upstream Wednesday and Thursday afternoons that may
move into our Delta Region each evening. The western portion of
stalled cold front will drift back north a bit Wednesday and
Thursday resulting in a chance for isolated storms over our
southwest each afternoon as well. A much drier airmass will reside
east of Mississippi and spread into our eastern zones limiting rain
chances there Wednesday and Thursday. Normal highs run near 87f.
Afternoon temperatures are expected to top out a couple degrees
above normal each afternoon.
Long term...Friday through next Tuesday...global models continue to
show decent agreement on the pattern evolution through the medium
range. The pattern will be one of transition with a northwest flow type
regime in place a we wrap up the week...followed by a brief period
of shortwave ridging...then a shift to a more amplified pattern for the
first half of next week with a eastern Continental U.S. Trough. What has
changed over the last 24 hours is now the Euro/GFS are in better
agreement now on the period for early next week. Timing is much
better on the trough amplification and southward push of a decent
late Sep cool front.
For Friday...the northwest flow pattern will help push a backdoor front into
part of the County Warning Area. Overall drier air will move in by Friday allowing for
less precipitation chances into Sat. Moisture will return for sun into Monday
as the larger trough takes shape and pushes a stronger front our
way. Better precipitation chances look to return for part of sun into early
Monday as moisture gets focused along and ahead of the front. There
area indications that the moisture could be on the high side as
leftover moisture from T.S. Odile may make its way into the regional
circulation as our frontal system takes shape early next week.
Temperatures will continue to run above climatology norms from Thu-sun. Some
locations (e/ne) may see lows near normal Friday morning but then warm
again over the weekend. Conditions look to shift to more seasonal
readings after the front with some potential for below normal
readings if the pattern can become more amplified. /Cme/