Windy and Warm Today


Thursday, March 17th 2011, 5:11 am
By: News On 6


I had a forecasted high of 76 yesterday and frankly didn't think I would be able to reach it due to the expected cloud cover in the afternoon.  Well, we did manage to hit the magic number despite the clouds and our ongoing forecast of even warmer air remains intact for the next 24 hours. And just like yesterday, the clouds will need to thin some this afternoon in order to reach the forecasted highs in the lower 80s.  The fire danger issues will continue to increase today and tomorrow before a weak cold front manages to slide across the area Friday evening

 The computer model guidance continues to offer dry conditions for our area, but I'm leaning toward adding a slight chance of showers and storms for early Friday morning and early Saturday morning across the northern third of the state.  Dew point temperatures in the 50s are streaming northward this morning and will continue to improve through tomorrow morning.  A low level jet (winds off the surface) is expected to develop overnight and feed into central Kansas.  This jet may be enough to spark off a few storms.  The actual cold front will approach the area Friday night and should stall around the I-40 corridor.  Early Saturday morning another low level jet formation may occur and this could also develop a few scattered storms.  Both of these probabilities would be around 20%.  At this hour (4AM) I probably will not add these small pops, but I do want to communicate this very low probability.

Relative humidity values will be in the lower 40s this afternoon along with gusty south winds of 20 to 30 mph.  The humidity values last Friday were down into the teens during the peak hours of extreme fire danger. The fire danger today and tomorrow will not be as extreme as last week due to this intrusion of low level moisture.  But We encourage you to remain very aware of the potential for rapid fire growth and fire spread.  Several counties remain under burn bans, but some counties are not included.  Even if your county is not included in an official burn ban, you should not burn. 

 The upper air pattern will transition to a southwest flow pattern and this will bring a chance of showers or storms to the region early next week.

The pattern would suggest a much higher chance of storms than our current forecast indicates.  But actual model output from most if not all of the operational models indicate very little chance for storm activity.  Why is this case?  The first thought remains that our storm system, currently off the west coast, is not being sampled correctly in the "start file" or initialization files.  This basically means the entire model output will be incorrect regarding precipitation chances Monday and Tuesday.  The system will not be sampled correctly until it is closer to the mainland.  The second thought deals with a capping issue.  What's a cap?

A cap is a stable layer of air aloft that does not allow the free transport of parcels into the atmosphere.  Many times the cap is a temperature inversion with warmer air aloft.  This stable layer can be seen on Skew-T data and also in computer model output data as CINH, or convective inhibition.  I think the hardest thing we do in the spring and early summer pattern is to determine cap strength.  Will the cap hold or will it break? 

The data for early next week indicates convective inhibition may be strong, so strong that it doesn't allow the convective process to mature.  I have included some fancy meteorological definitions for these terms:

  

Cap

(also called "Lid") A layer of relatively warm air aloft, usually several thousand feet above the ground, which suppresses or delays the development of thunderstorms. Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further and produce thunderstorms. As such, the cap often prevents or delays thunderstorm development even in the presence of extreme instability. However, if the cap is removed or weakened, then explosive thunderstorm development can occur.

The cap is an important ingredient in most severe thunderstorm episodes, as it serves to separate warm, moist air below and cooler, drier air above. With the cap in place, air below it can continue to warm and/or moisten, thus increasing the amount of potential instability. Or, air above it can cool, which also increases potential instability. But without a cap, either process (warming/moistening at low levels or cooling aloft) results in a faster release of available instability - often before instability levels become large enough to support severe weather development.

  

Convective Inhibition

(CIN or B-) - A numerical measure of the strength of "capping," typically used to assess thunderstorm potential. Specifically, it represents the cumulative effect of atmospheric layers the are warmer than the parcel moving vertically along the adiabat. Low level parcel ascent is often inhibited by such stable layers near the surface. If natural processes fail to destabilize the lower levels, an input of energy from forced lift (a front, an upper level shortwave, etc.) will be required to move the negatively buoyant air parcels to the point where they will rise freely. Since CIN is proportional to the amount of kinetic energy that a parcel loses to buoyancy while it is colder than the surrounding environment, it contributes to the downward momentum.

 From   weather.gov/glossary

  

confidence level:  Now through Saturday:  7

Issues:  Small pop chances.

 Next week:  6...issues possible storm formation.