Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260622_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)
=== ===== === ==== ==== === === === ====
Mon 06/22 06Z 0.13 2904  73  55  10 0.00
Mon 06/22 07Z 0.13 2604  73  52  10 0.00
Mon 06/22 08Z 0.22 2406  76  48  10 0.00
Mon 06/22 09Z 0.32 2509  78  43  10 0.00
Mon 06/22 10Z 0.33 2610  75  39   9 0.00
Mon 06/22 11Z 0.35 2609  71  36   9 0.00
Mon 06/22 12Z 0.29 2607  69  32   9 0.00
Mon 06/22 13Z 0.22 2405  67  29  10 0.00
Mon 06/22 14Z 0.22 2105  69  35  10 0.00
Mon 06/22 15Z 0.31 2006  70  35  10 0.00
Mon 06/22 16Z 0.48 2109  70  41  10 0.00
Mon 06/22 17Z 0.64 2113  74  74   9 0.00
Mon 06/22 18Z 0.42 2013  73  92   9 0.01
Mon 06/22 19Z 0.21 1913  76  97   8 0.02
Mon 06/22 20Z 0.15 1815  86  91   8 0.05
Mon 06/22 21Z 0.11 1718  92  86   9 0.08
Mon 06/22 22Z 0.12 1719  93  91   9 0.06
Mon 06/22 23Z 0.16 1520  93  95   9 0.03
Tue 06/23 00Z 0.28 1419  93  98   9 0.07
Tue 06/23 01Z 0.30 1317  92  99  10 0.11
Tue 06/23 02Z 0.34 1217  91  99  10 0.10
Tue 06/23 03Z 0.34 1217  94  99  10 0.05
Tue 06/23 04Z 0.31 1216  95  99  10 0.05
Tue 06/23 05Z 0.30 1214  96  98  10 0.06
Tue 06/23 06Z 0.21 1210  97  96  10 0.03
Tue 06/23 07Z 0.16 1006  96  95  10 0.01
Tue 06/23 08Z 0.15 0605  96  92  10 0.01
Tue 06/23 09Z 0.15 0307  95  87  10 0.01
Tue 06/23 10Z 0.13 0110  96  87  10 0.00
Tue 06/23 11Z 0.13 0111  96  86   9 0.00
Tue 06/23 12Z 0.13 0112  95  83   9 0.00
Tue 06/23 13Z 0.08 0013  92  74  10 0.00
Tue 06/23 14Z 0.07 0013  89  49  10 0.00
Tue 06/23 15Z 0.02 3513  89  38  10 0.00
Tue 06/23 16Z 0.06 3413  88  29  10 0.00
Tue 06/23 17Z 0.14 3415  86  23  10 0.00
Tue 06/23 18Z 0.24 3416  83  15  10 0.00
Tue 06/23 19Z 0.67 3316  80  11  10 0.00
Tue 06/23 20Z 0.95 3315  79   8  10 0.00
Tue 06/23 21Z 0.70 3316  83   8  10 0.00
Tue 06/23 22Z 0.30 3317  84   8  10 0.00
Tue 06/23 23Z 0.23 3318  82  10  10 0.00
Wed 06/24 00Z 0.40 3320  81  14  10 0.00
Wed 06/24 01Z 0.32 3320  86  14   9 0.00
Wed 06/24 02Z 0.28 3321  87  21   9 0.00
Wed 06/24 03Z 0.22 3322  86  20   9 0.00
Wed 06/24 04Z 0.16 3322  88  17   9 0.00
Wed 06/24 05Z 0.11 3420  91  20   9 0.00
Wed 06/24 06Z 0.05 3419  89  21   9 0.00
Wed 06/24 07Z 0.03 3417  87  21   9 0.00
Wed 06/24 08Z 0.04 3416  86  20   9 0.00
Wed 06/24 09Z 0.06 3416  86  24   8 0.00
Wed 06/24 10Z 0.09 3315  83  27   8 0.00
Wed 06/24 11Z 0.11 3315  84  28   8 0.00
Wed 06/24 12Z 0.15 3213  86  32   8 0.00
Wed 06/24 13Z 0.19 3213  88  38   8 0.00
Wed 06/24 14Z 0.19 3212  84  48   8 0.00
Wed 06/24 15Z 0.22 3212  82  46   8 0.00
Wed 06/24 16Z 0.31 3211  81  34   8 0.00
Wed 06/24 17Z 1.01 3111  83  29   8 0.00

Run total areal avg QPF for the Central_Greens is: 0.75 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