Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens
Model run: BTV_GRID_D2D_NAM3_20260212_0600
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 02/12 06Z 0.80 3320 93 73 -14 0.00
Thu 02/12 07Z 0.72 3322 95 69 -14 0.00
Thu 02/12 08Z 0.64 3323 95 67 -13 0.01
Thu 02/12 09Z 0.56 3322 95 65 -13 0.01
Thu 02/12 10Z 0.47 3321 94 64 -13 0.01
Thu 02/12 11Z 0.40 3421 93 62 -13 0.01
Thu 02/12 12Z 0.38 3421 94 63 -13 0.00
Thu 02/12 13Z 0.36 3421 94 68 -13 0.00
Thu 02/12 16Z 0.41 3319 93 59 -13 0.00
Thu 02/12 17Z 0.47 3220 93 51 -13 0.00
Thu 02/12 18Z 0.50 3220 93 29 -13 0.00
Thu 02/12 19Z 0.52 3221 92 10 -13 0.00
Thu 02/12 20Z 0.55 3221 89 6 -13 0.00
Thu 02/12 21Z 0.50 3222 76 10 -12 0.00
Thu 02/12 22Z 0.38 3323 66 12 -11 0.00
Thu 02/12 23Z 0.31 3424 66 13 -10 0.00
Fri 02/13 00Z 0.29 3424 71 14 -10 0.00
Fri 02/13 01Z 0.30 3424 72 14 -10 0.01
Fri 02/13 02Z 0.27 3423 71 14 -10 0.01
Fri 02/13 03Z 0.24 3421 69 14 -10 0.00
Fri 02/13 04Z 0.22 3419 67 15 -9 0.00
Fri 02/13 05Z 0.21 3418 64 17 -9 0.00
Fri 02/13 06Z 0.22 3318 61 20 -9 0.00
Fri 02/13 07Z 0.23 3317 60 22 -9 0.00
Fri 02/13 08Z 0.24 3217 61 28 -9 0.00
Fri 02/13 09Z 0.27 3218 64 32 -10 0.00
Fri 02/13 10Z 0.30 3118 65 30 -10 0.00
Fri 02/13 11Z 0.32 3119 66 30 -10 0.00
Fri 02/13 12Z 0.35 3120 69 18 -10 0.00
Fri 02/13 13Z 0.36 3021 72 14 -10 0.00
Fri 02/13 14Z 0.33 3019 73 16 -10 0.00
Fri 02/13 15Z 0.31 3017 75 19 -10 0.00
Fri 02/13 16Z 0.32 2917 77 19 -11 0.00
Fri 02/13 17Z 0.34 2917 77 17 -11 0.00
Fri 02/13 18Z 0.36 2917 75 18 -11 0.00
Fri 02/13 19Z 0.38 2816 73 35 -11 0.00
Fri 02/13 20Z 0.40 2816 71 63 -11 0.00
Fri 02/13 21Z 0.44 2717 68 52 -11 0.00
Fri 02/13 22Z 0.49 2719 66 44 -11 0.00
Fri 02/13 23Z 0.52 2719 62 50 -11 0.00
Sat 02/14 00Z 0.46 2619 55 55 -10 0.00
Sat 02/14 01Z 0.41 2618 49 52 -9 0.00
Sat 02/14 02Z 0.39 2618 49 62 -9 0.00
Sat 02/14 03Z 0.43 2618 58 65 -9 0.00
Sat 02/14 04Z 0.42 2618 59 67 -9 0.00
Sat 02/14 05Z 0.37 2617 83 81 -9 0.00
Sat 02/14 06Z 0.36 2616 93 80 -10 0.00
Sat 02/14 07Z 0.38 2615 95 86 -10 0.00
Sat 02/14 08Z 0.40 2714 96 89 -11 0.01
Sat 02/14 09Z 0.40 2814 96 86 -11 0.01
Sat 02/14 10Z 0.42 2815 96 86 -11 0.01
Sat 02/14 11Z 0.43 2815 96 86 -10 0.01
Sat 02/14 12Z 0.46 2816 96 88 -10 0.01
Sat 02/14 13Z 0.51 2918 95 85 -10 0.01
Sat 02/14 14Z 0.59 2920 96 84 -11 0.01
Sat 02/14 15Z 0.60 3020 97 34 -11 0.01
Sat 02/14 16Z 0.64 3019 97 16 -11 0.01
Sat 02/14 17Z 0.67 2919 90 27 -12 0.01
Run total areal avg QPF for the Northern_Greens is: 0.16 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