Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261015_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 10/15 18Z 0.07 3403  77   6   1 0.00
Thu 10/15 19Z 0.12 3203  77   5   2 0.00
Thu 10/15 20Z 0.13 3003  77   3   2 0.00
Thu 10/15 21Z 0.09 2903  70   3   3 0.00
Thu 10/15 22Z 0.05 2802  59   3   4 0.00
Thu 10/15 23Z 0.04 2801  47   3   5 0.00
Fri 10/16 00Z 0.02 1902  42   3   6 0.00
Fri 10/16 01Z 0.04 1805  45   3   6 0.00
Fri 10/16 02Z 0.06 1809  49   4   6 0.00
Fri 10/16 03Z 0.07 1812  52   5   6 0.00
Fri 10/16 04Z 0.10 1815  57  13   6 0.00
Fri 10/16 05Z 0.12 1819  62  38   6 0.00
Fri 10/16 06Z 0.15 1822  68  60   5 0.00
Fri 10/16 07Z 0.14 1825  65  93   5 0.00
Fri 10/16 08Z 0.19 1827  67  98   4 0.00
Fri 10/16 09Z 0.21 1829  77  98   5 0.01
Fri 10/16 10Z 0.19 1830  89  98   6 0.02
Fri 10/16 11Z 0.21 1834  97  98   6 0.10
Fri 10/16 12Z 0.21 1838  98  99   6 0.18
Fri 10/16 13Z 0.34 1941  98  97   6 0.16
Fri 10/16 14Z 0.43 2040  98  97   8 0.17
Fri 10/16 15Z 0.53 2040  99  88   9 0.08
Fri 10/16 16Z 0.54 2138  98  93  11 0.07
Fri 10/16 17Z 0.55 2135  99  94  12 0.05
Fri 10/16 18Z 0.58 2231  99  97  13 0.05
Fri 10/16 19Z 0.67 2330  98  97  13 0.08
Fri 10/16 20Z 0.65 2328  94  94  13 0.04
Fri 10/16 21Z 0.76 2331  94  92  12 0.03
Fri 10/16 22Z 0.89 2330  91  84  11 0.04
Fri 10/16 23Z 1.10 2335  97  77  11 0.05
Sat 10/17 00Z 1.28 2432  97  75  10 0.06
Sat 10/17 01Z 1.28 2534  95  70   9 0.06
Sat 10/17 02Z 1.08 2729  95  58   7 0.04
Sat 10/17 03Z 0.78 2827  97  58   4 0.03
Sat 10/17 04Z 0.71 2928  96  62   1 0.02
Sat 10/17 05Z 0.78 3027  96  56   0 0.01
Sat 10/17 06Z 0.55 3127  96  53  -2 0.01
Sat 10/17 07Z 0.42 3228  96  52  -2 0.01
Sat 10/17 08Z 0.32 3328  97  49  -3 0.01
Sat 10/17 09Z 0.29 3328  97  50  -4 0.01
Sat 10/17 10Z 0.27 3329  97  54  -4 0.01
Sat 10/17 11Z 0.40 3329  97  64  -5 0.01
Sat 10/17 12Z 0.43 3330  97  66  -6 0.01
Sat 10/17 13Z 0.45 3328  97  67  -6 0.01
Sat 10/17 14Z 0.48 3227  97  67  -7 0.01
Sat 10/17 15Z 0.43 3225  97  58  -7 0.01
Sat 10/17 16Z 0.46 3225  95  34  -8 0.00
Sat 10/17 17Z 0.77 3225  90   8  -8 0.00
Sat 10/17 18Z 4.00 3226  79   1  -9 0.00
Sat 10/17 19Z 8.25 3227  71   3  -9 0.00
Sat 10/17 20Z 8.36 3227  72   3  -9 0.00
Sat 10/17 21Z 7.20 3127  74   3  -9 0.00
Sat 10/17 22Z 5.40 3127  79   3  -9 0.00
Sat 10/17 23Z 1.64 3129  78   5  -9 0.00
Sun 10/18 00Z 1.82 3130  79   4  -9 0.00
Sun 10/18 01Z 1.44 3129  73   5 -10 0.00
Sun 10/18 02Z 0.74 3128  60   5  -9 0.00
Sun 10/18 03Z 0.57 3228  50  10  -9 0.00
Sun 10/18 04Z 0.51 3228  42  13  -8 0.00
Sun 10/18 05Z 0.52 3227  49  10  -8 0.00

Run total areal avg QPF for the Central_Greens is: 1.45 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