Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS63 KIND 252329
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
629 PM EST Sat Feb 25 2017

.UPDATE...

The Near Term and Aviation sections have been updated below.

&&

.SYNOPSIS...
Issued at 315 PM EST Sat Feb 25 2017

A return to winter weather for the weekend will be relatively short 
lived as southerly flow develops Sunday on the back side of high 
pressure. A transition to moist southwest flow aloft will bring a 
return to warmer temperatures and unsettled weather through the 
first half of next week. Cooler weather will again return later in 
the work week along with some opportunities for light snow.

&&

.NEAR TERM /Tonight/...
Issued at 629 PM EST Sat Feb 25 2017

Lowered min temp grids overnight and adjusted sky grids for latest
satellite trends. Otherwise forecast in good shape. Previous
discussion follows.

Issued at 315 PM EST Sat Feb 25 2017

Scattered flurries continue across portions of the forecast area 
this afternoon but there has been an overall diminishing trend over 
the last few hours as the upper wave axis shifts off to the east. 
Brutal reminder that it is technically still winter as temps have 
gone nowhere this afternoon. Running 40 to 45 degrees cooler than 
Friday with 18Z temps ranging from the upper 20s to mid 30s.

Back edge of the stratocu progressing east across Illinois. Should 
see some sun into western counties later this afternoon with 
clearing expanding east across the rest of central Indiana this 
evening as high pressure builds in. The gusty winds will also 
diminish during the evening as the pressure gradient relaxes with 
the deep low pressure lifting north towards James Bay. The high will 
track through the Tennessee Valley overnight with winds becoming 
light and variable then transitioning to southerly by daybreak 
Sunday.

Temps...coldest night in nearly 2 weeks on tap as temps drop into 
the lower 20s. May even see some teens in northern counties and 
normal cool spots. Cooler MAVMOS was preferred for lows.

&&

.SHORT TERM /Sunday through Tuesday/...
Issued at 315 PM EST Sat Feb 25 2017

Forecast challenges focus on precip chances for the early part of 
the week as a series of waves aloft track through the Ohio Valley 
followed by a stronger surface wave and frontal boundary arriving by 
the end of the period.

The upper level flow over the region will transition to a moist 
southwest regime by Monday and Tuesday as an upper trough develops 
over the western U S. The result will be a return to unsettled 
weather after a dry finish to the weekend...with much warmer 
conditions returning as well.

The high pressure will track into the central Appalachians but 
remain close enough to maintain dry conditions and plenty of 
sunshine across the region on Sunday. Warm advection will commence 
with the departure of the upper low late tonight and strengthen 
Sunday as southwesterly flow increases on the back side of the high 
pressure. Expecting mostly sunny skies with just some mid and high 
level clouds for much of the day. Clouds will increase near sunset 
and especially into the evening as a weak wave aloft tracks out of 
the Ozarks and into the Ohio Valley. Overall trends have been to 
focus forcing aloft with the wave near and south of the Ohio River 
Sunday night...with only subtle isentropic lift above 850mb serving 
as the primary mechanism to generate precip over parts of the 
region. Have cut back on low chance pops as a result and focused 
them mainly south of I-70 Sunday night and Monday morning. Model 
soundings do support potential for snowflakes to mix in with rain 
near the I-70 corridor but overall...low level thermals largely 
support rain as the main precipitation type. Amounts should only be 
a few hundredths of an inch by midday Monday.

Ridging will briefly reestablish for Monday afternoon before rain 
returns Monday night and Tuesday morning as a warm front surges 
north through the area. Considered adding a mention of isolated 
thunder with some elevated instability present with the 
boundary...but still some model disagreement present with respect 
to amount of instability and have left out for the time being. Will 
bring a mention of thunder in for later in the day Tuesday however 
as the region resides well into the warm sector south of the warm 
front and additional upper level energy moves into the Ohio Valley.

Temps...the onset of warm advection will bring a nice recovery in 
temperatures Sunday with most area rising into the mid and upper 
40s. Temps will warm further into the early part of the week with 
highs back into the 60s by Tuesday. Lows will return into the 40s by 
Monday night. With the monthly average temp at 43.5 degrees through 
Friday...the relatively quick return to above normal temps by Monday 
and Tuesday are likely to keep the average above the current monthly 
record of 42.3 degrees from 1882.

&&

.LONG TERM /Tuesday Night through Saturday/...
Issued at 142 PM EST Sat Feb 25 2017

A frontal system will slowly move through the Great Lakes during 
the long term. The forecast area will remain in 
southerly/southwesterly flow pattern, and this will bring small 
upper waves moving through the progressive upper flow pattern. The 
timing of the specific waves is up in the air, so confidence in 
these features decreases with time. Models are in good agreement 
though about the high probabilities for rain Tuesday night and 
Wednesday related to the surface front so will not adjust from 
initialization pops of likely to categorical. Extended models also 
show some instability available both Tuesday and Tuesday night, so 
will include from a slight chance to mid chance for thunder during 
that time.

The cold front is progged to move through Wednesday/Wednesday night, 
and temperatures will then return to near normal for Thursday 
through Friday night. Dry air should advect in along with the cold 
air Wednesday night, so chances for any precipitation decrease. 
However there are spokes of energy aloft moving through the main 
flow so could see small chances for a mix of rain/snow both late 
Wednesday night as well as Thursday night.

&&

.AVIATION /Discussion for the 26/00Z TAFs/...
Issued at 629 PM EST Sat Feb 25 2017

VFR through the period.

High pressure traversing the area will keep the weather quiet.
Initial stratocumulus over the area is gradually scattering out
and will likely do so within the first few hours of the period.

Winds may gust to near 20KT for another hour or two and then
subside overnight. Additional gusts to near 20KT will be possible
again tomorrow afternoon, out of the southwest rather than the
current west/northwest.

No obstructions to visibility are expected during the period.

&&

.IND WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SYNOPSIS...Ryan

National Weather Service Glossary of Abbreviations