NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260502_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)
=== ===== === ==== ==== === === === ====
Sat 05/02 12Z 0.12 1806  99  72  -1 0.00
Sat 05/02 13Z 0.11 2005  99  80  -1 0.03
Sat 05/02 14Z 0.23 2505  99  80  -2 0.03
Sat 05/02 15Z 0.32 2606  99  85  -2 0.01
Sat 05/02 16Z 0.38 2808  97  86  -2 0.01
Sat 05/02 17Z 0.57 2907  92  83  -2 0.00
Sat 05/02 18Z 1.40 2806  83  81  -2 0.00
Sat 05/02 19Z 3.74 2706  76  65  -1 0.00
Sat 05/02 20Z 3.11 2709  87  60  -1 0.00
Sat 05/02 21Z 0.88 2709  91  51  -1 0.02
Sat 05/02 22Z 0.50 2810  88  50  -2 0.01
Sat 05/02 23Z 0.55 2810  89  50  -2 0.00
Sun 05/03 00Z 0.64 2911  90  53  -2 0.00
Sun 05/03 01Z 0.58 2912  90  42  -3 0.01
Sun 05/03 02Z 0.49 3012  90  34  -3 0.00
Sun 05/03 03Z 0.38 3112  88  29  -4 0.00
Sun 05/03 04Z 0.32 3112  86  28  -4 0.00
Sun 05/03 05Z 0.27 3112  86  30  -4 0.00
Sun 05/03 06Z 0.22 3212  87  36  -4 0.00
Sun 05/03 07Z 0.16 3212  87  44  -4 0.00
Sun 05/03 08Z 0.14 3313  87  40  -4 0.00
Sun 05/03 09Z 0.14 3315  87  36  -5 0.00
Sun 05/03 10Z 0.16 3317  88  36  -5 0.00
Sun 05/03 11Z 0.17 3317  88  39  -5 0.00
Sun 05/03 12Z 0.23 3316  86  47  -5 0.00
Sun 05/03 13Z 1.16 3215  84  46  -5 0.00
Sun 05/03 14Z 3.07 3215  83  47  -5 0.00
Sun 05/03 15Z 4.30 3214  80  47  -4 0.00
Sun 05/03 16Z 5.05 3214  75  43  -4 0.00
Sun 05/03 17Z 5.50 3114  75  45  -3 0.00
Sun 05/03 18Z 5.26 3114  77  45  -3 0.00
Sun 05/03 19Z 5.83 3014  73  44  -3 0.00
Sun 05/03 20Z 6.67 3014  70  51  -3 0.00
Sun 05/03 21Z 7.82 2914  70  50  -2 0.00
Sun 05/03 22Z 7.27 2915  69  50  -2 0.00
Sun 05/03 23Z 3.88 2916  67  50  -2 0.00
Mon 05/04 00Z 1.96 2818  67  30  -2 0.00
Mon 05/04 01Z 1.78 2820  65  15  -2 0.00
Mon 05/04 02Z 1.49 2821  61   5  -2 0.00
Mon 05/04 03Z 1.13 2823  68  85  -2 0.00
Mon 05/04 04Z 0.88 2722  66  91  -1 0.00
Mon 05/04 05Z 0.75 2724  90  95  -1 0.02
Mon 05/04 06Z 0.83 2628  94  92   0 0.07
Mon 05/04 07Z 0.92 2531  90  92   0 0.04
Mon 05/04 08Z 0.96 2532  88  90   0 0.03
Mon 05/04 09Z 0.93 2632  87  83   1 0.01
Mon 05/04 10Z 0.94 2632  85  70   1 0.00
Mon 05/04 11Z 1.01 2532  85  26   0 0.00
Mon 05/04 12Z 1.09 2531  87  36   0 0.00
Mon 05/04 13Z 1.03 2530  90  85   1 0.00
Mon 05/04 14Z 0.89 2527  90  88   1 0.00
Mon 05/04 15Z 0.92 2523  91  85   1 0.00
Mon 05/04 16Z 1.09 2522  92  73   1 0.01
Mon 05/04 17Z 1.66 2522  91  44   1 0.00
Mon 05/04 18Z 3.60 2421  91  28   2 0.00
Mon 05/04 19Z 4.57 2421  90  29   2 0.00
Mon 05/04 20Z 5.48 2421  88  34   3 0.00
Mon 05/04 21Z 4.64 2421  88  26   3 0.01
Mon 05/04 22Z 2.59 2521  88  31   3 0.00
Mon 05/04 23Z 1.31 2421  89  34   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.31 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