wxgeek's weather-Spring Storm forecast-Update 4/9

Update Tue Apr 9

Our complex storm has split into two upper circulation centers, one in northeast UT and another in northeast AZ. Models really have not and still do not have a very good handle on this system. Apparently the storm is very mis-understood and is brooding in the Desert Southwest before moving on. Best guess is that the circulation center in AZ will become the primary center and move northeast across CO during the day today. As always, the track will determine how much additional snow we get. Surface low has developed in southwest CO, so again not the best location versus southeast CO or the TX panhandle. Current thinking is that the center will stay to the west of the foothills, so only limited additional snow, while the mountains will get the majority of the snow. Latest check of snow reports show most areas in the 2-5 inch range this morning, with highest snow report from Genesee of 7 inches. Very cold temps will also likely limit snowfall to mostly light snow. Upper flow still from the south, which is also not the best direction for heavy snow. With all that, I am thinking maybe an additional 2-5 inches of snow today for foothill areas. Snow may persist into the evening and nighttime hours, but should remain of light intensity. Cold temps have created slick driving conditions as initial snow melted and has now frozen. Temps to remain in the upper teens to low 20's on the plains today, and single digits to low teens in the foothills, so very cold temps for April. Overnight temps will be near or slightly below zero in the foothills, single digits on the plains. Strong northerly surface winds will continue today causing additional blowing and drifting of snow, especially east of I-25. Snow should dissipate after midnight foir all areas. Wednesday morning commute could still have some slick spots on roads.

Wednesday should be cool and mostly sunny by afternoon with a few lingering flurries over the south central mountains. Next weak system will move across CO Thursday, bringing a chance for showers across the mountains and into the foothills and adjacent plains by afternoon. Snow level 7000-8000 ft. Only little if an accumulation expected in the foothills, maybe a dusting to an inch in some areas, with 10-3 inches possible in the High Country. Repeat day on Friday with more showers possible. Slight warming trend into the weekend with temps back near seasonal norms, and some afternoon showers possible each day, mostly over the High Country with snow level 9000-10,000 ft. More precip chances mid to late next week.

As our current system moves east, severe weather threat will be high across the central and southern Plains on Wednesday, moving into the Mississippi Valley on Thursday. Severe thunderstorms and tornadoes will be possible across this area. We saw a glimpse of some severe weather across eastern CO Monday afternoon and evening with 4 tornadoes reported.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

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Update Mon Apr 8

A very interesting and complex Spring storm will affect CO beginning this afternoon and persist into Tuesday night. A very colorful NWS map of warnings and advisories now out (link to NWS map: http://www.crh.noaa.gov/den/ ). NWS has issued a Winter Storm Warning for much of western CO and now includes the foothills and Urban Corridor from 6 pm today through 6 pm Tuesday. Blizzard Warning has been issued for adjacent plains, with a Winter Storm Watch still in effect for eastern plains. System is currently located over southern NV and is beginning to spread showers and thunderstorms into western CO. Snow level currently around 11,000 ft and will remain high until colder arctic air moves south into CO later this evening and tonight. Before the main impact of this system, ahead of it we will have strong southerly winds this afternoon. Storm Prediction Center (SPC) has issued a slight risk area for severe thunderstorms across the far eastern plains of CO. As showers develop, atmospheric environment is favorable for severe thunderstorm development, with large hail and possible tornadoes this afternoon into early evening. Best chances for severe storms will be east of a Ft. Morgan to Limon line.

Now on to the ever evolving Spring storm. I am still not certain this will be a major snow maker for eastern CO. Latest model guidance has the upper level circulation splitting, with the northern branch moving farther north than previous model runs, and the southern branch remaining well south of our area. To me, this translates to lower snow amounts as the northern circulation never provides the deep upslope flow we need to produce major snow amounts. Flow aloft now expected to remain mostly southerly, with upslope northeast flow limited to about 10,000 to 12,000 ft. Latest models now have the upper level circulation moving into more west central CO by Tuesday morning versus the 4 Corners region and then move this area northeast into northeast CO Tuesday afternoon. This track is much less favorable than the upper low remaining to our south. However, since models have struggled with this system so much, confidence is still pretty low and the system will end up going wherever it wants. Cold front is still forecast to move south into CO this evening which will bring much colder temps across the state by Tuesday morning. Looks like snow level remains above 10,000 ft this afternoon, then begins to lower as cold front moves south this evening with snow level down to plains level by about midnight tonight. Snow will become possible in the foothills after about 6-8 pm.

Forecast now looks something like this. Precip will spread into western CO this afternoon with snow level at or above 10,000 ft. Showers will move east into the foothills and plains later this afternoon, with the chance for severe thunderstorms across the eastern plains late this afternoon into this evening. Snow will spread across CO this evening and tonight with snow level lowering to plains level by midnight. Snow may become heavy at times tonight into Tuesday with snowfall rates of 1-2 inches per hour possible at times. Strong northerly winds of 15-35 mph will accompany snow on Tuesday causing blowing and drifting of snow, especially east of I-25. Heaviest snow amounts expected to be in the foothills and Palmer Divide. Snow begins to dissipate Tuesday evening, ending by midnight. Snow amounts now look like this:

Mountains: 8-16 inches (heaviest amounts over the southwest mountains)
Foothills and Palmer Divide: 6-12 inches
Banana Belt: 4-8 inches
Urban Corridor: 4-9 inches
Eastern plains: 3-7 inches

If storm track takes a more northern track, snow amounts will be towards the lower end of these ranges. If it remains farther south, towards the higher end. Commute home tonight should be without issues, maybe just some wet areas in showers. By Tuesday morning, roads likely to be snow and ice packed above 7000 ft, with wet, slush and ice below that. Warm roads will melt initial snow, so ice likely to form underneath snow. Roads will be in better shape Tuesday evening, but may still have some slick spots at higher elevations. Temps will remain cold on Tuesday, with mid to upper 20's on the plains, and teen to low 20's in the foothills. By Tuesday night, some foothill locations will be close to zero.

Conditions improve Wednesday, although temps will remain cool. Next weak system will move across CO Thursday and bring a chance for showers Thursday afternoon into Friday morning. Snow level 9000 ft during the day Thursday lowering to 6000-7000 ft Thursday night. Only light if any snow accumulations expected for the foothills, possibly 1-3 inches for the High Country. Some showers also possible Friday afternoon with snow level 9000-10,000 ft. Weekend looks mostly dry, with some showers possible Sunday afternoon with snow level 8000-9000 ft.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

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Update Sun Apr 7

So models finally coming into better agreement, but as always still some differences. Showers moving across CO today, but should end by evening. System just coming onshore in the Pacific Northwest and will move into the Great Basin on Monday, near the 4 Corners by Tuesday morning and into northeast CO by Tuesday evening and then into western NE Wednesday morning. For CO, Monday will start out mostly sunny, but precip will move into western CO Monday afternoon with snow level initially around 10,000 ft. Snow will become heavy Monday night across western CO, and move into eastern CO Monday evening. For eastern CO, snow level initially 12,000 ft Monday afternoon, lowering to around 7000-8000 ft by midnight and down to plains level by Tuesday morning. Snow will be heavy at times from early Tuesday morning into Tuesday afternoon, gradually diminishing by Tuesday evening. Still some models like the ECMWF and now the GFS that split the energy in this system, some moving northeast into the Plains and some lingering over the southern Rockies. When this happens it tends to weaken the overall system. Nearly all models output around 1 inch of liquid equivalent with this system for our foothills. As system approaches Monday afternoon, some thunderstorms possible on the eastern plains, and rain showers for the foothills and Urban Corridor until snow levels lower Monday evening.

NWS has issued a Winter Storm Watch for much of eastern CO including the foothills, as well as mountain areas west of the Divide. They will update those to either warnings or advisories by Monday morning.For snow amounts, my best guess looks something like this:

Mountains: 8-16 inches
Foothills and Palmer Divide: 6-12 inches, with up to 14 inches in favored areas
Banana Belt: 4-8 inches
Urban Corridor: 4-10 inches
Eastern plains: 4-8 inches, highest amounts north of I-70

Snow should end by Tuesday night and be mostly sunny Wednesday. Commute back up the hill on Monday should be fine, maybe some rain showers. Tuesday morning could be tough. Snow will initially melt on warm roads, so as snow begins to accumulate, ice will form underneath. Roads likely to be a combination of wet, slushy, snow and ice packed during the day on Tuesday depending on your elevation. Commute back up the hill Tuesday evening could be slick as well, especially above 7000 ft. Roads in the Urban Corridor may remain wet to slushy on Tuesday. Temps will be much colder on Tuesday, with high temps near freezing on the plains, and in the 20's in the foothills.

Models indicate a chance for showers on Thursday, mostly west of the Divide but possible in the foothills and adjacent plains with snow level 7000-8000 ft. Slight chance for more showers Friday afternoon with snow level around 9000 ft. The upcoming weekend currently looks warm and dry across the state. More precip chances early next week.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

Bump for 4/8 Update

Bump for 4/9 update