Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260320_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)
=== ===== === ==== ==== === === === ====
Fri 03/20 00Z 0.46 2316  85   5  -7 0.00
Fri 03/20 01Z 0.56 2419  85   5  -6 0.00
Fri 03/20 02Z 0.64 2422  89  10  -6 0.01
Fri 03/20 03Z 0.71 2524  92  14  -6 0.01
Fri 03/20 04Z 0.72 2524  96  10  -6 0.02
Fri 03/20 05Z 0.84 2724  97   8  -7 0.01
Fri 03/20 06Z 0.90 2823  96  10  -7 0.01
Fri 03/20 07Z 0.80 2822  94   9  -7 0.00
Fri 03/20 08Z 0.63 2819  91   8  -7 0.00
Fri 03/20 09Z 0.52 2818  87   9  -6 0.00
Fri 03/20 10Z 0.41 2817  80  14  -5 0.00
Fri 03/20 11Z 0.31 2814  74  24  -4 0.00
Fri 03/20 12Z 0.25 2812  71  30  -4 0.00
Fri 03/20 13Z 0.23 2610  73  38  -4 0.00
Fri 03/20 14Z 0.21 2309  71  46  -4 0.00
Fri 03/20 15Z 0.16 2012  64  73  -3 0.00
Fri 03/20 16Z 0.20 2015  65  93  -2 0.00
Fri 03/20 17Z 0.23 1916  82  95  -3 0.00
Fri 03/20 18Z 0.11 1819  96  97  -2 0.03
Fri 03/20 19Z 0.16 1826  98  96   0 0.15
Fri 03/20 20Z 0.32 1929  99  97   0 0.16
Fri 03/20 21Z 0.49 2128  99  97   0 0.13
Fri 03/20 22Z 0.59 2228  99  96   1 0.13
Fri 03/20 23Z 0.60 2327  99  96   1 0.12
Sat 03/21 00Z 0.64 2327  99  87   1 0.09
Sat 03/21 01Z 0.63 2424  99  32   1 0.03
Sat 03/21 02Z 0.59 2422  99   5   1 0.03
Sat 03/21 03Z 0.53 2420  99   8   2 0.02
Sat 03/21 04Z 0.60 2521  99   9   1 0.04
Sat 03/21 05Z 0.51 2719  99   8   0 0.04
Sat 03/21 06Z 0.32 2915  98   9   0 0.02
Sat 03/21 07Z 0.17 3213  98   9   0 0.01
Sat 03/21 08Z 0.09 3314  97  10  -1 0.01
Sat 03/21 09Z 0.12 3315  97  18  -2 0.00
Sat 03/21 10Z 0.10 3319  95  25  -4 0.01
Sat 03/21 11Z 0.13 3323  94  58  -5 0.00
Sat 03/21 12Z 0.15 3323  91  67  -5 0.00
Sat 03/21 13Z 0.21 3325  92  62  -7 0.00
Sat 03/21 14Z 0.26 3325  92  53  -7 0.00
Sat 03/21 15Z 0.32 3225  92  28  -8 0.00
Sat 03/21 16Z 0.55 3224  93  10  -8 0.00
Sat 03/21 17Z 1.02 3223  93   4  -9 0.00
Sat 03/21 18Z 1.50 3222  93   1  -9 0.00
Sat 03/21 19Z 1.72 3221  93   3  -9 0.00
Sat 03/21 20Z 1.37 3220  92   2  -9 0.00
Sat 03/21 21Z 0.62 3220  87   5  -9 0.00
Sat 03/21 22Z 0.38 3219  80   6  -8 0.00
Sat 03/21 23Z 0.32 3219  74  14  -8 0.00
Sun 03/22 00Z 0.24 3218  66  22  -8 0.00
Sun 03/22 01Z 0.18 3317  58  29  -7 0.00
Sun 03/22 02Z 0.11 3313  48  46  -7 0.00
Sun 03/22 03Z 0.17 3212  48  58  -7 0.00
Sun 03/22 04Z 0.15 3110  43  80  -7 0.00
Sun 03/22 05Z 0.18 3009  43  88  -7 0.00
Sun 03/22 06Z 0.17 2806  42  93  -7 0.00
Sun 03/22 07Z 0.21 2606  42  93  -7 0.00
Sun 03/22 08Z 0.27 2308  48  92  -8 0.00
Sun 03/22 09Z 0.38 2107  79  90 -10 0.00
Sun 03/22 10Z 0.12 1907  92  91  -9 0.02
Sun 03/22 11Z 0.05 1709  93  90  -8 0.03

Run total areal avg QPF for the Central_Greens is: 1.13 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