Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260320_0600
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 06Z 0.55 2516  89   8  -6 0.00
Fri 03/20 07Z 0.67 2619  91   9  -7 0.00
Fri 03/20 08Z 0.62 2718  92  12  -7 0.00
Fri 03/20 09Z 0.56 2719  90  16  -7 0.00
Fri 03/20 10Z 0.55 2819  86  25  -6 0.00
Fri 03/20 11Z 0.41 2816  80  34  -5 0.00
Fri 03/20 12Z 0.28 2712  70  23  -3 0.00
Fri 03/20 13Z 0.22 2609  63   9  -3 0.00
Fri 03/20 14Z 0.25 2410  69  32  -4 0.00
Fri 03/20 15Z 0.23 2112  68  41  -3 0.00
Fri 03/20 16Z 0.31 2116  71  79  -3 0.00
Fri 03/20 17Z 0.33 2019  82  93  -2 0.00
Fri 03/20 18Z 0.25 1927  94  96   0 0.01
Fri 03/20 19Z 0.26 1931  93  91   2 0.03
Fri 03/20 20Z 0.46 2031  98  97   0 0.16
Fri 03/20 21Z 0.62 2134  98  96   1 0.17
Fri 03/20 22Z 0.88 2337  98  96   1 0.15
Fri 03/20 23Z 1.00 2437  98  92   1 0.13
Sat 03/21 00Z 1.02 2434  98  61   1 0.11
Sat 03/21 01Z 0.99 2530  98   7   0 0.08
Sat 03/21 02Z 0.93 2627  98   8   0 0.04
Sat 03/21 03Z 0.80 2724  98   9   0 0.03
Sat 03/21 04Z 0.64 2822  97  16  -1 0.02
Sat 03/21 05Z 0.39 2917  94  20  -2 0.01
Sat 03/21 06Z 0.31 2916  92  38  -2 0.01
Sat 03/21 07Z 0.24 3016  90  45  -2 0.01
Sat 03/21 08Z 0.20 3116  90  47  -3 0.00
Sat 03/21 09Z 0.15 3216  88  54  -3 0.00
Sat 03/21 10Z 0.14 3217  87  59  -4 0.00
Sat 03/21 11Z 0.16 3220  89  54  -5 0.00
Sat 03/21 12Z 0.16 3321  90  37  -6 0.00
Sat 03/21 13Z 0.15 3320  89  11  -7 0.00
Sat 03/21 14Z 0.16 3318  87   8  -7 0.00
Sat 03/21 15Z 0.23 3217  88  11  -8 0.00
Sat 03/21 16Z 0.30 3317  87  13  -8 0.00
Sat 03/21 17Z 0.27 3315  82  14  -7 0.00
Sat 03/21 18Z 0.45 3314  79  16  -7 0.00
Sat 03/21 19Z 0.68 3213  77  20  -7 0.00
Sat 03/21 20Z 0.50 3212  73  23  -7 0.00
Sat 03/21 21Z 0.20 3311  67  27  -7 0.00
Sat 03/21 22Z 0.12 3310  60  27  -6 0.00
Sat 03/21 23Z 0.10 3308  54  28  -6 0.00
Sun 03/22 00Z 0.08 3308  50  29  -6 0.00
Sun 03/22 01Z 0.08 3206  49  38  -6 0.00
Sun 03/22 02Z 0.11 3004  52  62  -6 0.00
Sun 03/22 03Z 0.12 2803  57  88  -6 0.00
Sun 03/22 04Z 0.11 2104  61  93  -5 0.00
Sun 03/22 05Z 0.11 2007  64  96  -5 0.00
Sun 03/22 06Z 0.17 2009  69  95  -5 0.00
Sun 03/22 07Z 0.21 2012  74  96  -5 0.00
Sun 03/22 08Z 0.31 2016  87  94  -6 0.00
Sun 03/22 09Z 0.27 2015  95  93  -6 0.05
Sun 03/22 10Z 0.23 1918  96  92  -5 0.07
Sun 03/22 11Z 0.26 1922  96  93  -4 0.06
Sun 03/22 12Z 0.22 1926  97  96  -3 0.05
Sun 03/22 13Z 0.26 1929  97  98  -2 0.08
Sun 03/22 14Z 0.25 1928  98  99  -1 0.11
Sun 03/22 15Z 0.31 1927  98  99  -2 0.11
Sun 03/22 16Z 0.34 2023  98  98   0 0.09
Sun 03/22 17Z 0.36 2121  99  98   0 0.10

Run total areal avg QPF for the Central_Greens is: 1.68 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