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Area forecast discussion 
National Weather Service Indianapolis in
304 am EDT Monday Apr 21 2014

the synopsis...near term and short term sections have been updated


issued at 304 am EDT Monday Apr 21 2014

Showers with embedded thunderstorms will develop later today and
continue tonight as a cold front moves through the Ohio Valley.
Cooler drier weather returns for Tuesday and Wednesday as high
pressure moves through the region. Warmer and more unsettled weather
returns for late week with the passage of another cold front. Behind
the front...cooler weather will return for the weekend.


Near term /today/...
issued at 304 am EDT Monday Apr 21 2014

Ridging aloft and at the surface remains in firm control over much
of the Ohio Valley early this morning. Middle and high level clouds are
steadily increasing from the west ahead of an upper wave and cold
front tracking through the Central Plains. With a light southeast
flow...temperatures generally ranged from the upper 40s to the middle 50s as
of 07z.

Main focus for today is the approach of the upper wave and cold
front to the west as low pressure off the North Carolina coast
finally shifts further east into the Atlantic Ocean. This will
enable the ridge axis to likewise shift east to the U S East Coast
by late day. Cloud coverage will increase throughout the day as
moisture advects into the region from the southwest. Weak lift and
forcing will move into the Ohio Valley during the course of the
afternoon with scattered showers and perhaps a thunderstorm
spreading east into the forecast area by late afternoon. More
expansive coverage to rainfall will likely hold off until this
evening as model soundings indicating it will take much of the day
to moisten the boundary layer. Will carry mainly low chance probability of precipitation for
middle/late afternoon.

Temperatures...filtered sun through the morning and warm advection ahead of
the front will enable another warm day peaking in the 70s. Low level
thermals supported maximum temperatures at or just above mavmos in the
middle/upper 70s.


Short term /tonight through Wednesday night/...
issued at 304 am EDT Monday Apr 21 2014

Forecast challenges focus on precipitation chances tonight as the front
swings through the region...and potential for frosty temperatures Wednesday

Weakening upper wave will track through the Ohio Valley with the
cold front tonight with rain showers and embedded thunderstorms.
Most widespread coverage expected during the evening and early
overnight...with precipitation gradually shifting into the southern/eastern
portions of the forecast area after 06z Tuesday. Brief period of
isentropic lift and subtle low level convergence within a narrow
ribbon of deeper moisture will be the main rainfall catalysts
tonight and will maintain likely probability of precipitation. Rainfall amounts will be
generally light at a quarter inch or less.

Cold front will be east of the forecast area by daybreak Tuesday
with the deeper moisture departing along with it. Expect skies to
clear quickly Tuesday morning as model soundings and relative humidity forecasts
indicating a rapidly drying column. Despite strong cold advection
and a sharp wave aloft passing through the lower Great Lakes during
the course of the day...expect any cumulus formation to be significantly
limited by the increasing subsidence and dry air advecting into the
region. Efficient low level mixing will bring stronger winds to the
surface Tuesday afternoon with maximum gusts up to 25 miles per hour.

High pressure ridge centers across the region Tuesday night with
northerly winds becoming light after midnight. With clear
skies...good radiational cooling setup for the region with potential
for frost accrual over much of the forecast area as temperatures fall into
the 30s. With the growing season having advanced enough across the
southern half of the forecast area...potential for frost headlines
early Wednesday. Will continue to highlight in the severe weather potential statement at this time.
Remainder of the short term will be dry with warm advection
commencing by late Wednesday as ridging aloft expands east into the
Ohio Valley. A warm front will lift across the forecast area
Wednesday night and may bring a brief increase in clouds. Any precipitation
associated with the warm front however should remain to the
northwest of the region.

Temperatures...mavmos guidance supported low level thermals for highs both
Tuesday and Wednesday...with temperatures slipping back into the 60s both
days over much of the forecast area. As mentioned above...Tuesday
night looking frosty as temperatures expected to fall into the 30s. Went
near MOS guidance for lows all three nights.


Long term /Thursday through Monday/...
issued at 231 am EDT Monday Apr 21 2014

Long term period will start with a frontal system approaching the
area. Model consistency still leaves a bit to be desired...but model
instability forecasts...along with convective precipitation forecasts...deep layer
shear and timing of frontal passage...suggest organized convection
may be a good bet late Thursday afternoon into the overnight. Will
have to monitor this potential as the week wears on.

Will remove allblend probability of precipitation Friday as frontal boundary will be well
east of the area and high pressure building into the area regardless
of model choice. Guidance brings another system into the area very
late in the period...but will temper these probability of precipitation a bit as model
inconsistencies are high.

Maximum temperatures needed bumped up a bit most periods as 850 temperatures
and low level thicknesses suggested allblend too cool.


Aviation /discussion for the 21/06z taf issuance/...
issued at 213 am EDT Monday Apr 21 2014

VFR through the first 3/4 of the period as a ridge of high pressure
across our area moves to the east. A frontal system will initiate
some showers and thunderstorms late in the period...this evening
through tonight which may cause some of the terminals to fall
below VFR. For now since uncertainty is high as to whether a
specific terminal will be impacted...went with thunderstorms in the vicinity and cumulonimbus groups
starting between 03-06z on the 22nd. Brought sites down to MVFR
during this time. Activity should clear the area by Tuesday morning
and skies should clear out and quickly come back up to VFR.

Otherwise for this morning broken high clouds. Today there may
be scattered cumulus by late morning with increasing middle/high clouds
during the day. Light south winds of 7 knots or less will become
southwest up to 12 knots this afternoon as a cold front approaches
from the northwest.


Ind watches/warnings/advisories...none.



near term...Ryan
short term...Ryan
long term...nield

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