Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260625_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)
=== ===== === ==== ==== === === === ====
Thu 06/25 12Z 0.17 2904  76  56  10 0.00
Thu 06/25 13Z 0.18 2703  75  54  10 0.00
Thu 06/25 14Z 0.41 2604  75  55  10 0.00
Thu 06/25 15Z 0.84 2404  73  54  10 0.00
Thu 06/25 16Z 1.79 2305  71  52  11 0.00
Thu 06/25 17Z 2.66 2306  70  57  11 0.00
Thu 06/25 18Z 3.29 2206  70  68  11 0.00
Thu 06/25 19Z 2.40 2106  70  77  11 0.00
Thu 06/25 20Z 2.03 2107  70  82  12 0.00
Thu 06/25 21Z 1.59 2107  68  79  12 0.00
Thu 06/25 22Z 0.99 2107  66  80  12 0.00
Thu 06/25 23Z 0.60 2208  69  85  12 0.00
Fri 06/26 00Z 0.40 2212  78  93  11 0.01
Fri 06/26 01Z 0.18 1912  76  92  11 0.02
Fri 06/26 02Z 0.17 1814  75  93  11 0.01
Fri 06/26 03Z 0.26 1917  78  91  11 0.00
Fri 06/26 04Z 0.34 1918  87  96  11 0.02
Fri 06/26 05Z 0.25 1917  92  97  10 0.09
Fri 06/26 06Z 0.21 1917  93  95  10 0.13
Fri 06/26 07Z 0.25 1919  95  92  11 0.16
Fri 06/26 08Z 0.31 2019  96  92  10 0.03
Fri 06/26 09Z 0.32 2018  93  86  11 0.01
Fri 06/26 10Z 0.28 2017  94  86  11 0.01
Fri 06/26 11Z 0.36 2018  96  91  10 0.14
Fri 06/26 12Z 0.36 2215  96  67  11 0.02
Fri 06/26 13Z 0.40 2315  95  75  11 0.01
Fri 06/26 14Z 0.38 2413  94  81  11 0.01
Fri 06/26 15Z 0.36 2411  93  62  11 0.00
Fri 06/26 16Z 0.38 2310  94  39  11 0.00
Fri 06/26 17Z 0.50 2311  94  33  11 0.00
Fri 06/26 18Z 0.71 2410  92  48  11 0.00
Fri 06/26 19Z 1.02 2412  89  51  11 0.00
Fri 06/26 20Z 0.81 2411  91  60  12 0.07
Fri 06/26 21Z 0.69 2512  93  64  12 0.16
Fri 06/26 22Z 0.61 2916  90  63  11 0.31
Fri 06/26 23Z 0.39 3015  85  54  12 0.05
Sat 06/27 00Z 0.34 3013  87  30  11 0.02
Sat 06/27 01Z 0.31 3012  90  30  11 0.00
Sat 06/27 02Z 0.29 2910  92  35  11 0.00
Sat 06/27 03Z 0.27 2810  93  34  11 0.01
Sat 06/27 04Z 0.28 2810  92  37  11 0.01
Sat 06/27 05Z 0.25 2910  91  34  11 0.01
Sat 06/27 06Z 0.22 3010  91  35  11 0.01
Sat 06/27 07Z 0.21 3010  92  39  11 0.01
Sat 06/27 08Z 0.15 3109  91  40  11 0.01
Sat 06/27 09Z 0.11 3208  89  41  11 0.01
Sat 06/27 10Z 0.11 3207  89  41  11 0.00
Sat 06/27 11Z 0.08 3206  88  46  11 0.00
Sat 06/27 12Z 0.09 3104  90  48  10 0.00
Sat 06/27 13Z 0.12 2904  92  51  10 0.00
Sat 06/27 14Z 0.10 2703  94  50  10 0.00
Sat 06/27 15Z 0.08 2502  96  48  10 0.00
Sat 06/27 16Z 0.08 2501  96  47  10 0.01
Sat 06/27 17Z 0.08 2601  94  46  10 0.02
Sat 06/27 18Z 0.05 2601  93  46  11 0.02
Sat 06/27 19Z 0.04 2601  92  43  11 0.01
Sat 06/27 20Z 0.05 2401  91  43  11 0.01
Sat 06/27 21Z 0.08 2302  92  44  11 0.01
Sat 06/27 22Z 0.05 2200  90  48  11 0.01
Sat 06/27 23Z 0.04 0101  91  60  11 0.03

Run total areal avg QPF for the Central_Greens is: 1.47 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