Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260310_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 03/10 00Z 0.83 2327 28 40 8 0.00
Tue 03/10 01Z 1.10 2331 28 43 8 0.00
Tue 03/10 02Z 1.11 2333 29 42 8 0.00
Tue 03/10 03Z 1.10 2433 31 39 8 0.00
Tue 03/10 04Z 1.12 2533 34 37 8 0.00
Tue 03/10 05Z 1.09 2634 37 42 9 0.00
Tue 03/10 06Z 1.01 2632 35 49 8 0.00
Tue 03/10 07Z 1.04 2731 34 51 8 0.00
Tue 03/10 08Z 1.05 2730 34 52 8 0.00
Tue 03/10 09Z 1.00 2727 38 51 8 0.00
Tue 03/10 10Z 0.89 2725 42 50 8 0.00
Tue 03/10 11Z 0.78 2722 46 52 8 0.00
Tue 03/10 12Z 0.66 2719 50 54 8 0.00
Tue 03/10 13Z 0.58 2616 52 55 8 0.00
Tue 03/10 14Z 0.56 2416 53 54 8 0.00
Tue 03/10 15Z 0.57 2317 54 45 8 0.00
Tue 03/10 16Z 0.63 2319 55 47 8 0.00
Tue 03/10 17Z 0.81 2220 56 42 7 0.00
Tue 03/10 18Z 1.14 2322 56 60 7 0.00
Tue 03/10 19Z 1.40 2322 61 42 7 0.00
Tue 03/10 20Z 1.43 2323 69 45 7 0.00
Tue 03/10 21Z 1.25 2423 80 44 8 0.00
Tue 03/10 22Z 0.95 2524 87 46 8 0.00
Tue 03/10 23Z 0.84 2524 93 47 8 0.02
Wed 03/11 00Z 0.63 2622 97 42 7 0.02
Wed 03/11 01Z 0.48 2819 98 39 7 0.02
Wed 03/11 02Z 0.31 2815 98 55 7 0.01
Wed 03/11 03Z 0.25 2914 98 71 7 0.01
Wed 03/11 04Z 0.20 2912 98 51 7 0.01
Wed 03/11 05Z 0.14 3009 98 59 7 0.01
Wed 03/11 06Z 0.06 3004 97 72 7 0.01
Wed 03/11 07Z 0.04 1701 97 71 7 0.00
Wed 03/11 08Z 0.03 1608 98 73 7 0.01
Wed 03/11 09Z 0.03 1615 98 70 8 0.01
Wed 03/11 10Z 0.03 1619 98 65 8 0.03
Wed 03/11 11Z 0.04 1625 98 60 8 0.03
Wed 03/11 12Z 0.06 1728 98 54 8 0.03
Wed 03/11 13Z 0.09 1730 98 52 9 0.03
Wed 03/11 14Z 0.09 1733 97 39 9 0.02
Wed 03/11 15Z 0.16 1836 97 73 9 0.03
Wed 03/11 16Z 0.19 1837 96 71 9 0.03
Wed 03/11 17Z 0.22 1939 97 75 10 0.03
Wed 03/11 18Z 0.24 1941 97 71 11 0.01
Wed 03/11 19Z 0.28 1942 93 84 11 0.02
Wed 03/11 20Z 0.33 2041 95 88 11 0.05
Wed 03/11 21Z 0.35 2041 93 95 12 0.01
Wed 03/11 22Z 0.44 2045 97 95 11 0.07
Wed 03/11 23Z 0.41 2045 94 93 11 0.06
Thu 03/12 00Z 0.51 2046 92 93 12 0.01
Thu 03/12 01Z 0.60 2145 92 81 12 0.01
Thu 03/12 02Z 0.68 2146 94 84 13 0.01
Thu 03/12 03Z 0.66 2144 92 91 13 0.02
Thu 03/12 04Z 0.91 2148 97 82 12 0.09
Thu 03/12 05Z 1.34 2345 97 80 10 0.04
Thu 03/12 06Z 1.21 2435 98 39 9 0.05
Thu 03/12 07Z 1.33 2433 98 53 7 0.06
Thu 03/12 08Z 1.31 2535 96 58 4 0.05
Thu 03/12 09Z 1.04 2436 91 72 3 0.01
Thu 03/12 10Z 1.23 2537 92 66 -1 0.01
Thu 03/12 11Z 1.49 2538 90 14 -5 0.01
Run total areal avg QPF for the Central_Greens is: 0.95 inches.
Froude Number (Frd#):
Frd# < 0.5 Flow is subcritical and blocked.
Upslope clouds/precip backed farther upwind of and up to mtn crest.
W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
Upslope clouds/precip falls immediately upwind of mtn crest.
W Upslope snow favors western slopes to the Green Mt. spine including:
Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
Gap winds possible.
Frd# 1-2 Flow is critical.
With strong winds, Mountain waves/downslope winds possible.
Precip falls close to mountain ridge crests and on lee side.
W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
Air flows freely over terrain.
Persistent upslope snow not favored. Scattered snow showers and flurries.
Relative Humidity (RH):
925-850 mb RH > 90% needed for upslope precipitation.
with 700mb RH > 70% favors upslope snow.
with 700mb RH > 90% greater amounts of W upslope snow possible.
850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
T > -11 10-15:1
T -11 to -15 25-35:1
T < -15 15-20:1