251 
fxus65 kgjt 191658 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
1058 am MDT Friday Mar 19 2010 


1050 am update...storm is generally evolving as prognosticated. The cold 
front is passing south of The Four-Corners this late morning. Some 
significant snow reports this morning include 2-11 inches on the 
north side of Uinta Mountains...6-8 Vail...3.5 at Gothic...and 4 inches at 
Steamboat Mountain that has blown away. The 700mb low is over Glenwood 
Canyon. The resultant east winds over the Park Range have been 30- 
40mph...but ski patrol has reported 70-75mph Middle Mountain. These winds 
will likely diminish the afternoon as the surface pressure gradient 
relaxes a bit and the 700mb low drops south along the western edge of 
the Continental Divide. 


Otherwise strong cold advection occurs today and tonight with 
500/700mb -32c/-14c cold core nestled over the Park Range by sunrise 
Saturday. Radar is already showing a popcorn effect of the 
convection. Most sites will see gusty northwest-NE winds through the day. A 
sliver of cape across the north-central holds the potential for heavy 
showers and even an isolated lightning strike. The 12z NAM and RUC 
both produce another 6 inches of snowfall today in the elks-west elks 
where warnings are valid. NE flow this evening may limit snowfall in 
the Highway 550 gorge in the northwest San Juans. Still expect some significant 
snowfall for Cerro Summit SW to Telluride. 


A cold night tonight under partially clearing skies and diminishing 
winds...with morning fog where significant showers occur today. 


&& 


Previous discussion... /issued 420 am MDT Friday Mar 19 2010/ 
short term...today through Saturday night... 


Fairly complicated pattern unfolding this morning through this 
afternoon. First the leading cold front associated with the present 
system has moved over the forecast area and at 3 am MDT was stretched 
from the northeast corner to the southwest corner. Precipitation has 
increased over the area early this morning as a result of this 
front...and of a leading shortwave in a deepening low pressure 
trough. A couple other shortwaves will to affect the region through 
the day and into tonight. These features show up well on infrared satellite 
loops. One has moved over the Arizona/NV/UT triple point and will continue 
southeast through the morning. The main energy associated with this 
impulse will go to our south...but general troughiness will keep the 
air mass unsettled over the southern portion. The other more 
northerly disturbance moved southeast across western Montana and is 
dropping into northwest Wyoming at this time. This impulse will drop 
across Wyoming and into our forecast area by midday. It will then work its 
way south-southeast reaching our southern border late this evening. 
Therefore precipitation will be fairly widespread throughout most of 
the day...diminishing from the west this evening. The main caveat to 
this scenario...is the easterly flow that will develop behind an 
initial 700mb low as it tracks from north to south along our eastern 
edge. This easterly flow will develop first over the Park Range this 
morning then spread southward through the day. 


By tonight activity will begin to wind down as the main trough tracks 
to the southeast. However a -32c cold core at 500mb following the 
northern shortwave will move across the north this evening. This will 
result in low level instability in the cold air...even as 700 mb 
temperatures drop to -12c. The limiting factor will be moisture as drier air 
moves over from the west-northwest. Fog possible in many valley 
locations in the wake of the storm late tonight and early Saturday 
morning. 


The system continues to move east on Saturday as a ridge of high 
pressure develops over the Great Basin. Lingering showers will be 
possible along The Divide...especially over the northern half. By 
Saturday night stability will increase...and the north flow relaxes 
as the ridge approaches from the west. 


After a recent taste of Spring...temperatures will fall below normal 
values during this period. 


Long term...Sunday through Friday... 


A strong ridge will continue migrating over the area and the 
Ridgeline will past overhead Sunday afternoon. Sunday night...the 
flow aloft becomes more zonal with middle and high level moisture 
advecting into the area from the west. Model differences become 
noticeable beginning Monday...in the development of the next trough. 
The GFS is initially more progressive with this trough. It closes off 
the 500 mb low further east /over slc/ Monday night...then digs the 
trough south-southeast through eastern Utah to The Four Corners Tuesday through Tuesday 
night. The European model (ecmwf) closes off the 500 mb low further northwest /over 
southern Idaho/ then tracks it south over central and western Utah 
before turning it to the east. 


Both models place the low center over The Four Corners about 12z Wednesday. 
The GFS continues to dig the trough to the south through eastern 
Arizona...before finally turning it to the east Wednesday evening. The European model (ecmwf) 
presents the more progressive solution on Wednesday as it moves the trough 
east along the Colorado/nm border to the panhandles by 00z Thursday. Ridging 
should bring drier conditions Friday. 


Have increased clouds...precip...and winds Monday night and Tuesday as the 
next system approaches...and blended the midrange model solutions. 


&& 


Aviation... 
as the cold front passes through the area from west to east...expect 
widespread MVFR ceilings and visibilities in rain and snow showers...with 
embedded IFR conditions...across the area. Some improvement will move 
in from the west this afternoon and tonight. 


&& 


Gjt watches/warnings/advisories... 


Colorado...Winter Storm Warning through 6 am Saturday morning for 
zone 10/12. 
Winter Weather Advisory through 6 am Saturday morning for 
zones 4/13/18 
Winter Weather Advisory through 6 PM Friday for zones 
3/9/17. 
Utah...Winter Storm Warning through midnight Friday for zone 23. 


&& 


$$ 


Update.......Joe 
short term...eh 
long term....cjc 
aviation.....Cjc 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)