Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260210_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 02/10 00Z 0.19 3221  53  69  -9 0.00
Tue 02/10 01Z 0.18 3222  56  68  -9 0.00
Tue 02/10 02Z 0.14 3222  55  70  -8 0.00
Tue 02/10 03Z 0.11 3321  54  73  -8 0.00
Tue 02/10 04Z 0.09 3319  54  79  -7 0.00
Tue 02/10 05Z 0.09 3318  57  83  -7 0.00
Tue 02/10 08Z 0.13 3215  84  89  -7 0.00
Tue 02/10 09Z 0.13 3113  87  88  -7 0.00
Tue 02/10 10Z 0.13 3112  85  87  -7 0.00
Tue 02/10 11Z 0.13 3111  80  85  -7 0.00
Tue 02/10 12Z 0.15 3010  72  82  -6 0.00
Tue 02/10 13Z 0.13 2907  58  72  -6 0.00
Tue 02/10 14Z 0.12 2706  43  58  -6 0.00
Tue 02/10 15Z 0.14 2507  36  54  -6 0.00
Tue 02/10 16Z 0.14 2307  33  47  -6 0.00
Tue 02/10 17Z 0.14 2207  33  49  -5 0.00
Tue 02/10 18Z 0.17 2109  31  69  -5 0.00
Tue 02/10 19Z 0.19 2111  36  91  -6 0.00
Tue 02/10 20Z 0.22 2013  63  94  -6 0.00
Tue 02/10 21Z 0.12 1815  81  94  -5 0.00
Tue 02/10 22Z 0.09 1818  94  94  -3 0.00
Tue 02/10 23Z 0.15 1922  95  94  -4 0.00
Wed 02/11 00Z 0.19 1923  95  96  -3 0.01
Wed 02/11 01Z 0.33 2025  96  98  -5 0.07
Wed 02/11 02Z 0.41 2124  97  97  -5 0.10
Wed 02/11 03Z 0.42 2222  97  98  -4 0.09
Wed 02/11 04Z 0.41 2320  97  95  -4 0.06
Wed 02/11 05Z 0.39 2418  98  85  -4 0.06
Wed 02/11 06Z 0.37 2416  98  37  -5 0.05
Wed 02/11 07Z 0.40 2516  98  18  -5 0.03
Wed 02/11 08Z 0.47 2617  97   9  -5 0.02
Wed 02/11 09Z 0.50 2718  97  19  -6 0.02
Wed 02/11 10Z 0.54 2819  98  29  -7 0.02
Wed 02/11 11Z 0.55 2920  97  45  -8 0.02
Wed 02/11 12Z 0.51 3021  96  65  -8 0.02
Wed 02/11 13Z 0.54 3021  96  74  -9 0.02
Wed 02/11 14Z 0.58 3021  95  80 -10 0.01
Wed 02/11 15Z 0.62 3021  94  82 -10 0.01
Wed 02/11 16Z 0.74 3020  93  81 -10 0.01
Wed 02/11 17Z 1.48 3019  94  82 -11 0.01
Wed 02/11 18Z 2.73 3018  94  84 -11 0.01
Wed 02/11 19Z 2.61 3018  94  86 -11 0.01
Wed 02/11 20Z 1.75 3019  95  88 -11 0.01
Wed 02/11 21Z 0.92 3120  95  86 -11 0.01
Wed 02/11 22Z 0.69 3223  96  85 -12 0.01
Wed 02/11 23Z 0.57 3225  96  83 -13 0.01
Thu 02/12 00Z 0.42 3325  96  82 -13 0.01
Thu 02/12 01Z 0.34 3326  95  81 -12 0.01
Thu 02/12 02Z 0.34 3326  96  81 -12 0.00
Thu 02/12 03Z 0.26 3324  96  81 -12 0.01
Thu 02/12 04Z 0.19 3324  95  80 -12 0.01
Thu 02/12 05Z 0.17 3324  95  79 -12 0.01
Thu 02/12 06Z 0.14 3325  93  76 -12 0.01
Thu 02/12 07Z 0.12 3426  92  75 -11 0.00
Thu 02/12 08Z 0.12 3326  92  75 -12 0.00
Thu 02/12 09Z 0.14 3326  93  73 -12 0.00
Thu 02/12 10Z 0.15 3327  94  73 -13 0.00
Thu 02/12 11Z 0.18 3327  94  74 -13 0.00

Run total areal avg QPF for the Central_Greens is: 0.75 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