NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250323_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)
=== ===== === ==== ==== === === === ====
Sun 03/23 06Z 3.61 3024  91  11 -17 0.00
Sun 03/23 07Z 3.20 3028  89   7 -17 0.00
Sun 03/23 08Z 2.93 3129  88   5 -18 0.00
Sun 03/23 09Z 1.82 3130  85   6 -18 0.00
Sun 03/23 10Z 1.09 3130  79   8 -17 0.00
Sun 03/23 11Z 0.86 3129  76   9 -17 0.00
Sun 03/23 12Z 0.70 3227  72   8 -17 0.00
Sun 03/23 13Z 0.63 3226  68   6 -16 0.00
Sun 03/23 14Z 0.61 3224  65   5 -16 0.00
Sun 03/23 15Z 0.61 3222  61   5 -16 0.00
Sun 03/23 16Z 0.67 3120  57   5 -16 0.00
Sun 03/23 17Z 0.74 3118  53   6 -15 0.00
Sun 03/23 18Z 0.67 3116  47   8 -14 0.00
Sun 03/23 19Z 0.60 3014  42  10 -14 0.00
Sun 03/23 20Z 0.69 2915  41  11 -13 0.00
Sun 03/23 21Z 0.63 2816  39  11 -12 0.00
Sun 03/23 22Z 0.55 2916  37  10 -11 0.00
Sun 03/23 23Z 0.53 2917  37   9 -11 0.00
Mon 03/24 00Z 0.36 2914  34   8  -9 0.00
Mon 03/24 01Z 0.26 3012  30   7  -7 0.00
Mon 03/24 02Z 0.22 2910  30   9  -7 0.00
Mon 03/24 03Z 0.15 2807  28  12  -6 0.00
Mon 03/24 04Z 0.11 2507  29  16  -6 0.00
Mon 03/24 05Z 0.06 2208  29  20  -6 0.00
Mon 03/24 06Z 0.02 1909  26  22  -4 0.00
Mon 03/24 07Z 0.04 1913  25  20  -4 0.00
Mon 03/24 08Z 0.07 1819  24  25  -3 0.00
Mon 03/24 09Z 0.10 1824  25  51  -3 0.00
Mon 03/24 10Z 0.15 1828  35  89  -3 0.00
Mon 03/24 11Z 0.20 1732  65  96  -2 0.00
Mon 03/24 12Z 0.22 1735  85  98  -3 0.01
Mon 03/24 13Z 0.25 1740  88  96  -3 0.03
Mon 03/24 14Z 0.21 1840  89  84  -3 0.03
Mon 03/24 15Z 0.16 1837  90  42  -3 0.01
Mon 03/24 16Z 0.12 1833  92  25  -3 0.01
Mon 03/24 17Z 0.13 1830  94  11  -3 0.01
Mon 03/24 18Z 0.10 1927  95  11  -3 0.01
Mon 03/24 19Z 0.10 1824  95   9  -2 0.01
Mon 03/24 20Z 0.06 1921  95  10  -2 0.01
Mon 03/24 21Z 0.03 1919  95  10  -2 0.01
Mon 03/24 22Z 0.04 2015  95   7  -2 0.01
Mon 03/24 23Z 0.06 2112  94  17  -3 0.00
Tue 03/25 00Z 0.06 2109  92  17  -2 0.00
Tue 03/25 01Z 0.11 2209  92  68  -3 0.00
Tue 03/25 02Z 0.21 2311  97  91  -3 0.01
Tue 03/25 03Z 0.40 2514  93  92  -4 0.06
Tue 03/25 04Z 0.54 2416  88  81  -4 0.01
Tue 03/25 05Z 0.51 2318  92  83  -5 0.00
Tue 03/25 06Z 0.56 2418  98  87  -6 0.01
Tue 03/25 07Z 0.77 2419  89  85  -7 0.01
Tue 03/25 08Z 0.86 2421  92  84  -7 0.00
Tue 03/25 09Z 0.80 2422  93  83  -8 0.00
Tue 03/25 10Z 0.65 2421  93  83  -7 0.01
Tue 03/25 11Z 0.76 2422  93  84  -8 0.00
Tue 03/25 12Z 0.82 2522  93  83  -8 0.00
Tue 03/25 13Z 0.92 2520  94  81  -8 0.00
Tue 03/25 14Z 1.00 2418  94  81  -8 0.00
Tue 03/25 15Z 0.95 2417  95  84  -8 0.00
Tue 03/25 16Z 1.00 2417  95  84  -7 0.01
Tue 03/25 17Z 0.80 2417  95  83  -7 0.01

Run total areal avg QPF for the Northern_Greens is: 0.28 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