NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260430_1800
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)
=== ===== === ==== ==== === === === ====
Thu 04/30 18Z 0.24 2705  99  96   1 0.00
Thu 04/30 19Z 0.29 2706  99  96   2 0.01
Thu 04/30 20Z 0.32 2808  99  93   2 0.02
Thu 04/30 21Z 0.36 3011  98  92   2 0.04
Thu 04/30 22Z 0.41 3116  98  90   0 0.04
Thu 04/30 23Z 0.31 3217  96  87   0 0.01
Fri 05/01 00Z 0.33 3217  95  81   0 0.00
Fri 05/01 01Z 0.34 3218  94  74   0 0.00
Fri 05/01 02Z 0.33 3218  93  68  -1 0.00
Fri 05/01 03Z 0.30 3218  93  70  -1 0.00
Fri 05/01 04Z 0.33 3218  94  69  -1 0.01
Fri 05/01 05Z 0.33 3218  95  70  -1 0.01
Fri 05/01 06Z 0.34 3219  95  74  -2 0.01
Fri 05/01 07Z 0.35 3219  95  77  -2 0.00
Fri 05/01 08Z 0.35 3219  94  80  -2 0.00
Fri 05/01 09Z 0.34 3219  94  79  -3 0.00
Fri 05/01 10Z 0.32 3218  93  71  -3 0.00
Fri 05/01 11Z 0.30 3217  90  61  -3 0.00
Fri 05/01 12Z 0.32 3216  89  53  -3 0.00
Fri 05/01 13Z 0.50 3215  88  46  -3 0.00
Fri 05/01 14Z 2.03 3213  86  37  -3 0.00
Fri 05/01 15Z 3.19 3112  82  37  -3 0.00
Fri 05/01 16Z 3.85 3111  80  31  -2 0.00
Fri 05/01 17Z 4.21 3010  77  31  -2 0.00
Fri 05/01 18Z 4.81 3010  75  28  -1 0.00
Fri 05/01 19Z 3.85 3009  70  32   0 0.00
Fri 05/01 20Z 3.22 3008  64  35   0 0.00
Fri 05/01 21Z 2.24 3006  60  32   0 0.00
Fri 05/01 22Z 1.51 3105  60  35   0 0.00
Fri 05/01 23Z 0.47 3004  62  36   0 0.00
Sat 05/02 00Z 0.22 2803  63  45   0 0.00
Sat 05/02 01Z 0.18 2502  64  55   0 0.00
Sat 05/02 02Z 0.07 1701  65  56   0 0.00
Sat 05/02 03Z 0.08 1703  66  72   0 0.00
Sat 05/02 04Z 0.06 1705  66  84   0 0.00
Sat 05/02 05Z 0.09 1506  65  86   0 0.00
Sat 05/02 06Z 0.12 1508  63  90   0 0.00
Sat 05/02 07Z 0.17 1610  72  94   0 0.01
Sat 05/02 08Z 0.11 1712  85  92  -1 0.01
Sat 05/02 09Z 0.07 1712  92  81  -1 0.01
Sat 05/02 10Z 0.13 1812  97  69  -1 0.01
Sat 05/02 11Z 0.24 2012  99  63  -1 0.01
Sat 05/02 12Z 0.33 2310  99  57  -2 0.01
Sat 05/02 13Z 0.36 2509  98  49  -2 0.00
Sat 05/02 14Z 0.34 2609  96  47  -2 0.00
Sat 05/02 15Z 0.33 2608  95  57  -2 0.00
Sat 05/02 16Z 0.37 2708  95  49  -2 0.00
Sat 05/02 17Z 0.44 2706  93  47  -2 0.00
Sat 05/02 18Z 0.63 2805  89  57  -2 0.00
Sat 05/02 19Z 1.17 2904  85  46  -1 0.00
Sat 05/02 20Z 0.98 3003  79  36  -1 0.00
Sat 05/02 21Z 0.68 3002  77  40   0 0.00
Sat 05/02 22Z 0.47 3103  79  58   0 0.00
Sat 05/02 23Z 0.16 3204  84  61  -1 0.00
Sun 05/03 00Z 0.10 3305  87  62  -1 0.00
Sun 05/03 01Z 0.07 3406  88  68  -1 0.00
Sun 05/03 02Z 0.05 3507  90  76  -1 0.00
Sun 05/03 03Z 0.05 3509  93  78  -2 0.00
Sun 05/03 04Z 0.09 0011  95  68  -2 0.00
Sun 05/03 05Z 0.13 0011  95  72  -2 0.01

Run total areal avg QPF for the Central_Greens is: 0.22 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