NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260321_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)
=== ===== === ==== ==== === === === ====
Sat 03/21 00Z 0.36 2413  99  82   0 0.00
Sat 03/21 01Z 0.31 2511  97  30   0 0.01
Sat 03/21 02Z 0.29 2312  97   5   0 0.00
Sat 03/21 03Z 0.36 2314  98   4   0 0.00
Sat 03/21 04Z 0.45 2516  99   7   0 0.01
Sat 03/21 05Z 0.41 2716  99   9   0 0.01
Sat 03/21 06Z 0.30 2915  99  11  -1 0.02
Sat 03/21 07Z 0.20 3115  98  12  -1 0.02
Sat 03/21 08Z 0.14 3216  97  16  -2 0.01
Sat 03/21 09Z 0.12 3317  97  30  -4 0.01
Sat 03/21 10Z 0.13 3318  95  45  -5 0.00
Sat 03/21 11Z 0.12 3320  91  49  -6 0.00
Sat 03/21 12Z 0.10 3321  87  40  -7 0.00
Sat 03/21 13Z 0.09 3422  84  32  -7 0.00
Sat 03/21 14Z 0.10 3421  82  29  -7 0.00
Sat 03/21 15Z 0.13 3319  78  20  -8 0.00
Sat 03/21 16Z 0.21 3317  76  15  -8 0.00
Sat 03/21 17Z 0.53 3316  75  13  -8 0.00
Sat 03/21 18Z 0.88 3217  74  12  -7 0.00
Sat 03/21 19Z 0.42 3315  70  10  -7 0.00
Sat 03/21 20Z 0.37 3314  68  12  -7 0.00
Sat 03/21 21Z 0.21 3213  64  12  -6 0.00
Sat 03/21 22Z 0.20 3212  59  16  -6 0.00
Sat 03/21 23Z 0.16 3210  57  35  -6 0.00
Sun 03/22 00Z 0.14 3107  61  67  -6 0.00
Sun 03/22 01Z 0.13 2904  65  94  -5 0.00
Sun 03/22 02Z 0.18 2306  71  94  -5 0.00
Sun 03/22 03Z 0.19 2205  90  94  -7 0.00
Sun 03/22 04Z 0.05 1805  93  91  -6 0.02
Sun 03/22 05Z 0.17 2010  94  93  -6 0.02
Sun 03/22 06Z 0.26 2016  90  97  -5 0.03
Sun 03/22 07Z 0.31 2019  90  97  -5 0.02
Sun 03/22 08Z 0.29 1922  97  97  -4 0.02
Sun 03/22 09Z 0.21 1923  97  98  -3 0.04
Sun 03/22 10Z 0.13 1825  97  99  -2 0.07
Sun 03/22 11Z 0.11 1827  97  99  -2 0.10
Sun 03/22 12Z 0.16 1826  98  98  -2 0.08
Sun 03/22 13Z 0.26 1924  98  96  -1 0.08
Sun 03/22 14Z 0.32 2022  98  93   0 0.07
Sun 03/22 15Z 0.37 2221  98  93   0 0.07
Sun 03/22 16Z 0.37 2319  98  77   1 0.03
Sun 03/22 17Z 0.45 2419  98  57   1 0.02
Sun 03/22 18Z 0.51 2517  98  40   0 0.03
Sun 03/22 19Z 0.60 2617  99  31   0 0.03
Sun 03/22 20Z 0.55 2816  98  23  -1 0.02
Sun 03/22 21Z 0.44 3017  98  20  -2 0.02
Sun 03/22 22Z 0.22 3218  96  21  -3 0.01
Sun 03/22 23Z 0.09 3419  94  20  -3 0.01
Mon 03/23 00Z 0.04 3419  94  20  -4 0.00
Mon 03/23 01Z 0.07 3516  94  21  -5 0.00
Mon 03/23 02Z 0.10 0015  94  23  -6 0.00
Mon 03/23 03Z 0.11 0016  92  21  -5 0.00
Mon 03/23 04Z 0.16 0116  90  21  -5 0.00
Mon 03/23 05Z 0.20 0116  89  23  -6 0.00
Mon 03/23 06Z 0.19 0115  88  26  -6 0.00
Mon 03/23 07Z 0.22 0215  88  25  -7 0.00
Mon 03/23 08Z 0.22 0214  91  31  -8 0.00
Mon 03/23 09Z 0.27 0314  93  37  -9 0.00
Mon 03/23 10Z 0.28 0314  94  38  -9 0.00
Mon 03/23 11Z 0.28 0314  95  44 -10 0.00

Run total areal avg QPF for the Central_Greens is: 0.88 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