Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261017_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)
=== ===== === ==== ==== === === === ====
Sat 10/17 06Z 0.54 3225  97  51  -2 0.00
Sat 10/17 07Z 0.60 3229  94  46  -4 0.00
Sat 10/17 08Z 0.60 3231  95  44  -4 0.00
Sat 10/17 09Z 0.66 3230  95  43  -5 0.00
Sat 10/17 10Z 0.63 3230  94  26  -6 0.00
Sat 10/17 11Z 0.61 3230  94   5  -6 0.00
Sat 10/17 12Z 0.67 3230  96   0  -7 0.00
Sat 10/17 13Z 0.58 3228  96   1  -7 0.00
Sat 10/17 14Z 0.57 3225  95   3  -8 0.01
Sat 10/17 15Z 0.53 3223  92   3  -8 0.00
Sat 10/17 16Z 0.53 3222  84   3  -8 0.00
Sat 10/17 17Z 0.45 3220  77   3  -8 0.00
Sat 10/17 18Z 0.57 3219  71   6  -8 0.00
Sat 10/17 19Z 0.67 3119  66  19  -8 0.00
Sat 10/17 20Z 0.58 3220  63  29  -7 0.00
Sat 10/17 21Z 0.43 3220  59  31  -6 0.00
Sat 10/17 22Z 0.36 3220  52  27  -6 0.00
Sat 10/17 23Z 0.35 3222  46  32  -5 0.00
Sun 10/18 00Z 0.32 3221  41  46  -5 0.00
Sun 10/18 01Z 0.27 3220  37  42  -4 0.00
Sun 10/18 02Z 0.23 3219  38  43  -4 0.00
Sun 10/18 03Z 0.19 3217  40  48  -3 0.00
Sun 10/18 04Z 0.18 3215  42  48  -3 0.00
Sun 10/18 05Z 0.23 3115  45  44  -3 0.00
Sun 10/18 06Z 0.30 3015  48  51  -3 0.00
Sun 10/18 07Z 0.37 3016  49  53  -3 0.00
Sun 10/18 08Z 0.40 2915  49  56  -3 0.00
Sun 10/18 09Z 0.40 2916  52  62  -3 0.00
Sun 10/18 10Z 0.35 3017  60  60  -2 0.00
Sun 10/18 11Z 0.33 3017  66  60  -1 0.00
Sun 10/18 12Z 0.30 3016  68  54   0 0.00
Sun 10/18 13Z 0.26 3015  68  48   0 0.00
Sun 10/18 14Z 0.24 3013  69  45   0 0.00
Sun 10/18 15Z 0.24 2911  67  42   1 0.00
Sun 10/18 16Z 0.25 2810  63  39   1 0.00
Sun 10/18 17Z 0.28 2710  53  35   1 0.00
Sun 10/18 18Z 0.29 2710  40  30   2 0.00
Sun 10/18 19Z 0.31 2711  35  27   3 0.00
Sun 10/18 20Z 0.32 2612  32  29   4 0.00
Sun 10/18 21Z 0.32 2713  30  29   5 0.00
Sun 10/18 22Z 0.30 2714  27  29   6 0.00
Sun 10/18 23Z 0.26 2712  24  33   7 0.00
Mon 10/19 00Z 0.24 2711  19  30   8 0.00
Mon 10/19 01Z 0.22 2710  14  26   8 0.00
Mon 10/19 02Z 0.22 2610  11  19   8 0.00
Mon 10/19 03Z 0.22 2610  10  15   9 0.00
Mon 10/19 04Z 0.23 2611  11  14   9 0.00
Mon 10/19 05Z 0.23 2511  13  15   9 0.00
Mon 10/19 06Z 0.23 2611  13  14  10 0.00
Mon 10/19 07Z 0.23 2611  14  15  10 0.00
Mon 10/19 08Z 0.24 2611  15  15  10 0.00
Mon 10/19 09Z 0.24 2612  16  15  10 0.00
Mon 10/19 10Z 0.24 2711  16  15  10 0.00
Mon 10/19 11Z 0.22 2710  15  16  10 0.00
Mon 10/19 12Z 0.20 2809  15  17  10 0.00
Mon 10/19 13Z 0.18 2808  14  18  10 0.00
Mon 10/19 14Z 0.17 2807  14  15  10 0.00
Mon 10/19 15Z 0.15 2807  14  14  11 0.00
Mon 10/19 16Z 0.14 2806  15  15  11 0.00
Mon 10/19 17Z 0.13 2805  16  16  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.01 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