Forecasting Clues Flashcards
How is advection and winds related?
Advection occurs when winds blow across the isotherms
How can rain warm temps?
Downward motion of rain can aid in mixing down warmer temps from aloft. However must be weary of Evap cooling
Name features of a “bowling ball” vorticity signature:
- Not much advection
- Main precip band isn’t overhead
- usually south and east
- Winds won’t mix down if vort goes overhead location
Be careful using 700 VV maps 48+ hours out. Look at overall synoptic pattern
Look to use high res HRRR model for short term
How does damming affect wind speed?
When air is dammed, not a lot of mixing at beginning of event leading to lower winds
How do you analogous forecast?
- Find where 24 hours out forecast is on current map
- Locate synoptic scale features
- Temps will be similar but account for snow cover, wind off water, downsloping/upsloping (warmer/cooler)
How much faster do models come in from what they say? Not including high res
~3 hours
If you think a front is going to pass through before the model then stick with that for all parameters!!
Don’t forecast precip coming through early if you don’t forecast the temps to come through as well
Read model diagnostic. See what model they pick for a system
Go with what model initialized better and stick with it
What are the characteristics of a cold conveyor belt snow storm?
- Synoptic scale
- Bands of cold and snow are NW of surface and 850mb low
- Often yield heavy snow especially when mesoscale bands embedded within storm
What are examples of warm and cold conveyor belt storms
Warm- Alberta clipper
Cold- Nor’easter
What are some characteristics of a warm conveyor belt storm?
- Less accumulation ~2-6”
- Short lived but still can have impressive snowfall rates
- Followed by FZRA/PL on large cyclones
What are forecasting tips for figuring out snowfall amounts?
- Look at QPF
- Temp- cold enough to snow?
- Temp- when heavy precip, models often too warm-> consider wet bulb via skew t
- Ratios: Cold conveyor- 8:1 to 20:1
Warm conveyor for strong cyclone 7:1 to 15:1
Warm conveyor for Alberta clipper 15:1 to 25:1
What surface temp gives us best heavy flakes?
-12C to -16C
What are general rules of thumb for 850mb temp forecasting?
Summer: if sunny add 13-18C If cloudy add 6-13C Winter: If sunny add 9-13C If cloudy add 2-9C
When is it best to use 850 temp method?
When conditions are similar to previous day such as same cloud cover, same winds, and same synoptic setup
What is helicity and what values of helicity are good for severe storms?
Helicity: wind shear changes with height
150-300: potential for storms
300-400: supercells are favorable
400+: tornadoes are possible
How are LI values related to severe weather?
- 2: weak
- 3 to -5: moderate
- 6 or less: strong
How are SSI related to severe weather?
+3 to +1: rain with possible storms
+1 to -2: thundershowers
-3 to -6: severe thunderstorms
<-6: severe storms and possible tornadoes
How are KI indexes related to thunderstorm probabilities?
15-19: 0-20%
20-30: 20-60%
30-40: 60-90%
40: 90-100%
How are TT related to thunderstorm events?
44-48: non-severe thunderstorms
49-55: some severe storms
>55: severe thunderstorms with possible tornadoes
How does CIN relate to thunderstorm development?
High values of CIN (-50) impede/cap thunderstorm development where low values (-10) allow for storms to break through the CIN and develop
What teleconnection do we want to see in the summer for decent weather?
-NAO
What does the PNA and NAO indicate?
Positive PNA and negative NAO leads to ridging in the west and trough in the east
Negative PNA and positive NAO is trough in the west and ridge in the east
How to distinguish forming front? Dying front?
Forming- dashed lines with triangles/circles on each dash
Dying- dashed lines with breaks between each circle/triangle
