Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service Jackson MS
1001 am CST sun Mar 1 2015

Update...its a bit warmer out this morning with temperatures running
around 10 to 15...even 20 degrees higher than 24 hours. This comes
thanks to an increase in moisture across the region. 12z kjan
sounding indicates about an inch in precipitable water values and
this is also indicative by the lower 50s dewpoints across many
locations. These dewpoints are some 25 to 30 degrees moister than
yesterday. Area radars show a couple of areas of rain moving to the
northeast into and across the arklamiss. The first being along and
north of the Highway 82 corridor. Most of this is light to moderate
rain. Further south moving into the Natchez area is a cluster of
heavier rain with some thunderstorms. This has actually shown a
little bit of a robust nature indicating it could have contained some
sub severe hail. All rain/storm activity is moving to the northeast
through this morning. Hi-res model guidance indicates that this will
continue through the day and may increase some in coverage.
Temperatures will be on the warmer side again today but given the
cloud cover and rain...we likely wont see highs nearing 70 degrees
like we did yesterday areawide. Going forecast handles much of the
short term well and only made some minor adjustments to account for
going trends. I did add some thunder to the weather grids as well to
account for what is occurring this morning.

The main focus for the afternoon package will be on the wintry
weather in the extended period/middle week. First indications are that the
potential is still there as noted in the last few model runs. Details
will be ironed out with the new 12z data coming in. /28/

&&

Aviation...this taf period will be one of persistent IFR/MVFR
ceilings with on/off rain showers and -ra. The focus will be to time some
precipitation in the first 6 hours as best possible and become more general
with time. Due to a surface front across the area for the next 24-36
hours...surface winds will be a challenge as to determine direction...but
overall winds will mainly be less than 8-10kts. The exception will
be glh where north/NE winds closer to 15 kts look to develop later
tonight into early Monday. /Cme/



&&

Previous discussion... /issued 430 am CST sun Mar 1 2015/

Short term...today through Monday night...cloudy and wet with
milder temperatures through the short term period. Early morning
surface analysis had the large 1040mb high centered over the middle
Atlantic Seaboard and wedging back to the southwest over the
southeast states. An inverted trough was noted from the Texas coast
stretching northeast across our County Warning Area and over the Tennessee Valley.
The surface high will shift east off the East Coast today but
continue to ridge back across the Gulf Coast states and try to nudge
the inverted surface trough to the northwest. A northern stream
shortwave will swing east across the northern plains today and the
Great Lakes region tonight. This will help drop a >1035mb surface
high over the Central Plains tonight that will work to keep the
inverted trough in place. Meanwhile...west to southwest flow aloft
over our region aided by a closed low spinning off the California
coast will help deep moisture increase over our County Warning Area. This moisture
increase and the presence of the inverted trough will lead to
widespread rainfall by this afternoon that will continue through
Monday night. The 00z sun Jan sounding had a precipitable water around a half an
inch. Precipitable waters will increase today and be near 1.4 inches areawide by
this evening. The northeast flow west of the trough will hold
temperatures down in the lower 50s today but the southeast flow east
of the surface trough will help temperatures climb into the middle 60s.
Tonight into Monday the Central Plains surface high will shift east
and become centered over the Ohio Valley by Monday evening. This
will result in the surface boundary becoming west to east oriented
over our County Warning Area and drop just south of Interstate 20. Warmer
temperatures in the 60s are expected south of the boundary Monday
afternoon while the northern half of our County Warning Area will be held in the
50s. The surface high will shift to the East Coast by Tuesday
morning while ridging aloft strengthens over our County Warning Area from the Gulf
Monday night. This will help the boundary lift north as a weak warm
front resulting in warmer than normal morning lows Tuesday morning.
/22/

Long term...Tuesday through Saturday...continued rain chances
followed by potential winter weather and a shot of much colder air
highlight the extended portion of the forecast.

The upper level pattern to begin the period will feature upper
troughing extending across The Rockies into the southwest with upper
ridging over the east. The surface warm front will have lifted north
across the area...with steady low level warm advection ahead of a
developing surface low over the middle Mississippi Valley and a cold
front trailing into the Southern Plains. Isolated to scattered
showers will be possible during this time frame aided by isentropic
ascent and passing weak shortwaves. Thunder also cannot be ruled out
in this time frame given weak instability. Though the warm air advection regime
will likely promote widespread low clouds it should still allow
temperatures to rise into the 70s across most of the area Tuesday even
given the reduced insolation.

Heading into Wednesday...the upper trough will nudge farther east
with an amplifying upper jet streak (approaching 200 knots max)
extending from the Lower Plains through the Great Lakes region). The
associated surface cold front will begin moving into the area during
the day Wednesday. There are some timing differences still to be
reconciled between available guidance...with the GFS indicating a
faster frontal passage than the Euro and Gem. Ahead of the front models are
depicting surface based instability...thus thunderstorms will be
possible...with the greater likelihood over the southeast half of
the area where timing would seemingly allow for more daytime heating
ahead of the front.

The airmass behind this front will be quite a shock to the system
given the warmer temperatures anticipated over the early portion of the
week. With the strong jet maximum still remaining northwest of the
region...strong upper divergence will promote continued large scale
lift with considerable Post frontal precipitation. As early as Wednesday
afternoon...rain could change over to freezing rain and/or sleet
over portions of the Delta as subfreezing temperatures surge
southward. There will be a warm nose to erode in the 700-900 mb
layer...but the substantial depth of low level cold air modeled in
bufr soundings would be sufficient for at least some refreezing
above the surface.

Wednesday night...latest indications are that the surface freezing
line/p-type transition will continue to translate farther south and
east toward the I-20 corridor. The GFS hints at the potential for
frozen precipitation even farther south. As we are still ramping up wintry
precipitation potential in the forecast...opted to lean toward the
slower/less aggressive European model (ecmwf) approach. Meanwhile farther north and
west...a transition to more sleet or snow is possible as the warm
nose erodes. We will continue to highlight winter weather potential
in severe weather potential statement/graphicast products but will maintain fairly generic language
given the inherent uncertainty this far out. Obviously there are
still many details to work out in the coming days.

Thursday will be a raw day across the entire area. With lingering
clouds and strong cold advection...temperatures will struggle to get
out of the 30s in most locations. Wintry precipitation will remain possible
over the northern two thirds of the County Warning Area mainly during the morning
and northerly winds will be blustery making it feel even colder.

At the end of the week as the upper jet hangs up near or just north
of the region...we will be stuck in the transition between surface
high pressure/colder air to the north and passing surface systems to
the south. The GFS remains fairly dry through this time frame...
keeping most quantitative precipitation forecast to our south. However the Euro suggests the
potential for precipitation over the southern half of the area
throughout this period. This pattern could create some potential for
an additional shot at wintry precipitation at some point. Right now there
is far too much uncertainty...and only rain will be mentioned
through the remainder of the forecast pending better model
agreement. /Dl/

&&

Preliminary point temps/pops...
Jackson 65 51 56 55 / 91 79 72 45
Meridian 65 53 59 53 / 73 67 64 42
Vicksburg 64 47 55 54 / 97 83 71 45
Hattiesburg 68 57 69 58 / 71 38 47 34
Natchez 65 51 59 56 / 96 75 67 38
Greenville 51 39 50 48 / 100 89 70 45
Greenwood 57 43 51 50 / 96 93 70 51

&&

Jan watches/warnings/advisories...
MS...none.
La...none.
Arkansas...none.
&&

$$

28/cme/22/dl

National Weather Service Glossary of Abbreviations