Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
1014 am EDT sun may 3 2015
The near term section has been updated below.
issued at 300 am EDT sun may 3 2015
Warm and dry weather will be back again today. However...a cold
front will approach from the northwest and bring increased humidity
to central Indiana beginning Monday. There will also be thunderstorm
chances Monday through Tuesday...mainly north of Bloomington and
Columbus as the front stalls out and creeps north as a warm front.
The remainder of the week will remain warm with more thunderstorm
chances for the weekend.
Near term /rest of today/...
issued at 1014 am EDT sun may 3 2015
Vorticity center currently in eastern Iowa is expected to move into
southern Wisconsin later today based on short term guidance. Been a
few echoes on the radar this morning...but appears little of this is
reaching the ground. Cloud cover this morning should thin out over
the next several hours given satellite trends upstream.
This morning/S upper air suggests highs today may be a couple of
degrees warmer than the current forecast. Will nudge up the forecast
highs a bit.
Today looks to be a repeat of yesterday with the exception of being
slightly warmer and more humid.
Models in good agreement that broad surface high pressure over the
Appalachians will settle southeast to just off the Carolina coast
this afternoon. This will allow for increased southwest winds off
the Gulf. Meanwhile...broad upper trough will be moving east and
skirting the Canadian and U.S. Prairies as a broad upper ridge
remains in tact further south over the central states. Upper wave
in advance of the Central Ridge will be moving east and southeast
across central Indiana this morning and was currently producing a
decent amount of middle and upper level cloud cover over Illinois and
Indiana. Model relative humidity time sections show some middle level moisture hanging
around even through the afternoon. Steep lapse rates and manageable
convective temperatures suggest there could be some fair weather cumulus
around as well. Weak echoes over Illinois overnight were at best
producing sprinkles...and with low levels starting off dry...will
not mention any probability of precipitation.
That all said...partly cloudy skies should suffice today. With
southwest winds around 10 knots and gusts to near 20 knots and with
model 850 millibar temperatures warming another degree to 11 to 12
degrees celsius...should see temperatures a degree or two warmer
than yesterday with highs in the middle and upper 70s looking
good. This is a degree or so below 00z MOS and ensemble MOS.
Short term /tonight through Tuesday night/...
issued at 300 am EDT sun may 3 2015
The main challenges to the short term will be 1) timing
thunderstorms as they move into northwestern parts of central
Indiana morning morning 2) how far south to take probability of precipitation and finally 3)
will a front return far enough north to keep a dry forecast on
Tuesday night? Subtle model differences in frontal position along
with potential convective feedback issues and potential outflow
considerations all make precise convective evolution difficult and
lead to a low confidence detailed forecast. Thus...do not want to
rock the boat too much and prefer only minor changes.
Models are in general agreement that a broad upper trough will
progress eastward and straddle the Canadian and U.S. Border. The
trough should move to the Lake Superior and u.P. Vicinity by 12z
Monday and into Quebec by 00z Tuesday. This should allow a cold
front to drop southeast to southeastern Wisconsin and southwestern
Kansas by 12z Monday and to just north of a Fort Wayne to Lafayette
line at 00z Tuesday. At that time...the models have the front
stalling before building southeast upper ridge forces it back north
as a warm front on Tuesday.
Looking at the model quantitative precipitation forecast fields...the 00z GFS and to a lesser degree
the 00z Gem are the quickest with both bringing it into our
northwestern forecast area by 12z Monday. The other models and
previous forecast hold off until after 12z Monday. The GFS and Gem
may be overdoing outflow. So...for that reason and consistency will
keep probability of precipitation out tonight and rather just bring increasing clouds
overnight from northwest to southeast.
After that...model general consensus minus an outlier or two
suggest going with probability of precipitation across all but our far southern tier on
Monday and Monday night with the best chances across the
north...closer to the front. Models then gradually shift quantitative precipitation forecast
fields further north and consensus is for a dry forecast by Tuesday
Areas from northern Vermillion to northern Hamilton and Randolph
have been placed in a marginal risk for severe weather Monday
afternoon and evening. Model mixed layer convective available potential energy prognosticated from 800 to
1200 j/kg in this time peiod. However...shear looks rather weak.
So...do not expect more than an isolated severe storm.
00z GFS MOS looks a bit too warm...but with 850 millibar level
warming to 13 to 14 degrees celsius...the slightly not as warm
00z NAM looks good with highs in the upper 70s and lower 80s. Lows
will be around 60.
Long term /Wednesday through Sunday/...
issued at 237 am EDT sun may 3 2015
Guidance continues to indicate upper level ridging centered just
southeast of the area middle to late week. This should suppress
precipitation across the region. Will have to remove some spotty low
probability of precipitation from the initialization early in the long term.
Frontal system will begin to impinge upon the area late week into
the weekend which will necessitate chance probability of precipitation.
Temperatures will be among the warmest of the season thus far with
80 degrees in play pretty much every day. Intialization handled this
well and few changes were required.
Aviation /discussion for the 03/12z tafs/...
issued at 700 am EDT sun may 3 2015
VFR through the period.
Expect ample middle level cloud across the area today...with some
scattered cumulus underneath. Winds will generally be
southerly...and may gust to near 20kt this afternoon. Gusts will
subside in typical diurnal fashion this evening.
No visibility concerns through the period.
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