NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260417_1200
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)
=== ===== === ==== ==== === === === ====
Fri 04/17 12Z 0.03 3514  84  74   8 0.00
Fri 04/17 13Z 0.04 3513  84  82   7 0.00
Fri 04/17 14Z 0.06 0011  80  81   8 0.00
Fri 04/17 15Z 0.05 3510  77  73   8 0.00
Fri 04/17 16Z 0.04 3510  74  60   8 0.00
Fri 04/17 17Z 0.05 3511  71  50   8 0.00
Fri 04/17 18Z 0.08 0011  67  42   8 0.00
Fri 04/17 19Z 0.14 0010  65  34   8 0.00
Fri 04/17 20Z 0.20 0110  62  26   8 0.00
Fri 04/17 21Z 0.18 0110  60  21   8 0.00
Fri 04/17 22Z 0.17 0209  58  17   8 0.00
Fri 04/17 23Z 0.22 0310  55  12   8 0.00
Sat 04/18 00Z 0.27 0411  51   9   8 0.00
Sat 04/18 01Z 0.28 0611  50   6   9 0.00
Sat 04/18 02Z 0.27 0811  54   3   9 0.00
Sat 04/18 03Z 0.21 1109  63   5   8 0.00
Sat 04/18 04Z 0.13 1309  71   8   8 0.00
Sat 04/18 05Z 0.14 1412  76   9   8 0.00
Sat 04/18 06Z 0.15 1415  79   9   8 0.00
Sat 04/18 07Z 0.21 1417  74   8   8 0.00
Sat 04/18 08Z 0.23 1419  63   7   8 0.00
Sat 04/18 09Z 0.15 1417  55   6   8 0.00
Sat 04/18 10Z 0.15 1418  54   6   7 0.00
Sat 04/18 11Z 0.15 1519  54   7   7 0.01
Sat 04/18 12Z 0.17 1421  57   7   7 0.01
Sat 04/18 13Z 0.15 1522  61   6   7 0.01
Sat 04/18 14Z 0.13 1519  65   6   6 0.01
Sat 04/18 15Z 0.14 1521  67   7   7 0.00
Sat 04/18 16Z 0.15 1522  73   8   7 0.00
Sat 04/18 17Z 0.17 1523  76  10   7 0.01
Sat 04/18 18Z 0.15 1522  75  12   7 0.01
Sat 04/18 19Z 0.12 1523  72  13   8 0.00
Sat 04/18 20Z 0.08 1623  69   4   9 0.00
Sat 04/18 21Z 0.03 1623  68   9   9 0.00
Sat 04/18 22Z 0.04 1724  70   8   9 0.00
Sat 04/18 23Z 0.08 1725  74   6   9 0.00
Sun 04/19 00Z 0.10 1826  77   7  10 0.00
Sun 04/19 01Z 0.12 1827  78  26  10 0.00
Sun 04/19 02Z 0.19 1928  74  30  11 0.00
Sun 04/19 03Z 0.22 1928  74  36  11 0.00
Sun 04/19 04Z 0.37 2030  86  56  10 0.00
Sun 04/19 05Z 0.38 2129  92  55   9 0.00
Sun 04/19 06Z 0.44 2131  97  83   9 0.03
Sun 04/19 07Z 0.38 2128  98  93   9 0.05
Sun 04/19 08Z 0.46 2227  99  91   7 0.04
Sun 04/19 09Z 0.48 2223  98  94   6 0.05
Sun 04/19 10Z 0.53 2320  99  97   4 0.06
Sun 04/19 11Z 0.59 2718  99  98   1 0.07
Sun 04/19 12Z 0.42 3021  98  99  -1 0.05
Sun 04/19 13Z 0.31 3120  97  99  -1 0.10
Sun 04/19 14Z 0.39 3021  97  99  -2 0.07
Sun 04/19 15Z 0.43 3022  97  98  -3 0.05
Sun 04/19 16Z 0.44 3022  91  98  -4 0.01
Sun 04/19 17Z 0.59 3022  94  94  -6 0.03
Sun 04/19 18Z 0.49 3019  89  82  -6 0.04
Sun 04/19 19Z 0.50 3118  75  59  -6 0.00
Sun 04/19 20Z 0.65 3017  71  10  -6 0.00
Sun 04/19 21Z 1.60 2815  87  12  -6 0.00
Sun 04/19 22Z 0.95 2817  89  19  -6 0.00
Sun 04/19 23Z 1.12 2819  87  25  -6 0.00

Run total areal avg QPF for the Central_Greens is: 0.71 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