Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New Orleans la
757 am CST Wednesday Dec 4 2013
gpt and stennis continue to report dense fog with visibility down to a
quarter mile. With surface dewpoint in the middle 60s and sea surface
temperatures on the Mississippi Sound in the upper 50s...sea fog was
expected to develop. South winds have displaced the low dect and
fog north onto the Mississippi coast. Lifting is expected between
9 and 10 am.
Previous discussion... /issued 441 am CST Wednesday Dec 4 2013/
latest surface analysis showed a 997mb low over Oklahoma with
southerly flow from Red Valley to Georgia. Over the northern
plains...single digits to sub zero temperatures has started to spill
south. Pressure gradient was relatively tight with 4mb change
across the forecast area. While higher dewpoints of the middle 60s
are in place...boundary layer winds remain from 10 to 15
knots...hostile environment for radiational fog and cloud cover
does not help. Waters temperatures on tidal lakes and near shore waters
remain in the upper 50s. Surface winds have decreased slightly and
ceiling have descended from 1.1kft to 0.7kft at Lakefront. South
winds have displaced this moisture and conditions are worst off as
far as sea fog north half of the Lake Pontchartrain this morning.
Upper level analysis continue to show a trough axis from North
Dakota to California and southwest to west flow from southwest
Continental U.S. To the Middle Atlantic States. Precipitable plots showed values
around 1 inch lix and east...0.8 inch at lch and Jan...and 0.6
inch at shv.
low level moisture is expected surge north over the lower
Mississippi Valley with precipitable water values increasing to 1.5 over the
forecast area late tonight. Model sounding through late today
through late Thursday night revealed an inversion present from 4
to 8kft. This may prevent deep convective development but low top
isolated showers can not be ruled out today or tonight. Surface
low over Oklahoma will lift north and allow cold dense air to dive
south over central and Southern Plains today through Thursday.
Meanwhile at upper level...several disturbance will maintain a
positively tilted trough axis in place today through Sunday.
Ergo...southwest flow will remain in play from Texas to east Continental U.S.
And produce moisture and precipitation along and north of this front
boundary Friday through Saturday. The cold front will enter the
northwest zones Friday morning and push into the coastal waters
Saturday. The main upper level trough will finally lift east. In
response...a surface low may try to develop along over the
northwest Gulf by Sunday track north and allow the front boundary
southeast again through the forecast area on Monday.
Temperatures will remain warm through early Friday...dive Friday night
through Saturday...slight warming Sunday to early Monday and
finally cooling again late Monday through Wednesday of next week.
Periods of mostly rain...some thunder...is expected Thursday night
through Saturday morning and another round Saturday through
Monday. Positively tilted trough will stretched the strength of
the system and strongest dynamics should remain north of the area
through this package and severe weather is not anticipated but
periods of rain is on The Table with heavy rainfall especially on
Friday and Friday night. 18
fog seems to be slow to develop across the area as boundary layer
winds have not weakened very much. They could slack off enough for
MVFR visible to develop around sunrise but that/S about it. Middle to low
level clouds will prevail through the period. South winds of 5 to 10
knots will continue and similar conditions as tonight expected
current synopsis shows surface ridge centered in the western
Atlantic extends well into the central Gulf of Mexico. A surface low
is developing along a cold front near the Texas/OK/KS borders. This low
will race northeast along the front. The pressure gradient between
the trough and ridge will keep winds right around 12 to 15 knots
over the offshore coastal waters. Will hold off on exercise caution
headline as conditions appear to marginal. Ridge will hold strong
for as long as it can as the cold front approaches the area.
Expecting winds/seas to remain stagnant through the end of the week.
The cold front should move into the the coastal waters Friday night
into Saturday morning but stall across the outer waters as the upper
trough to the north will already be racing northeast. The boundary
will temporarily lift back north Sunday lending to onshore flow.
This regime will be short lived as a stronger upper trough will send
a secondary front will into the Gulf of Mexico Monday morning.
Models suggest that this secondary surge will be stronger than
previously thought and a longer duration of small craft conditions
will persist Monday through possibly middle week.
Decision support services (dss) code legend
green = no weather impacts that require action
blue = long fused watch/warning/advisory in effect or high
yellow = heightened impacts with short fused
watch/warning/advisory issuances; radar support
Orange = high impacts - slight to moderate risk severe; nearby
tropical events; hazmat or other large episodes
red = full engagement for moderate to high risk severe
and/or direct tropical threats; events of National
Preliminary point temps/pops...
mcb 76 66 78 65 / 20 20 40 50
btr 80 66 79 67 / 20 20 40 50
asd 78 66 77 67 / 20 20 30 30
msy 79 67 77 69 / 20 20 30 30
gpt 76 66 74 67 / 20 20 30 20
pql 77 66 76 68 / 20 20 20 20
MS...dense fog advisory until 9 am Wednesday for the following zones: