NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260221_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 02/21 06Z 0.13 2008  97  85  -6 0.00
Sat 02/21 07Z 0.27 2210  99  75  -7 0.00
Sat 02/21 08Z 0.33 2409  99  83  -7 0.01
Sat 02/21 09Z 0.34 2510  99  95  -7 0.01
Sat 02/21 10Z 0.29 2709  98  94  -7 0.02
Sat 02/21 11Z 0.21 2908  98  93  -7 0.02
Sat 02/21 12Z 0.16 3006  99  89  -7 0.01
Sat 02/21 13Z 0.11 3004  99  81  -7 0.01
Sat 02/21 14Z 0.06 3202  99  72  -7 0.01
Sat 02/21 15Z 0.06 0001  99  65  -7 0.00
Sat 02/21 16Z 0.08 0000  99  66  -7 0.00
Sat 02/21 17Z 0.09 2400  99  72  -7 0.01
Sat 02/21 18Z 0.08 2600  99  72  -7 0.01
Sat 02/21 19Z 0.10 0402  98  65  -7 0.01
Sat 02/21 20Z 0.15 0304  98  60  -7 0.00
Sat 02/21 21Z 0.18 0404  96  57  -8 0.00
Sat 02/21 22Z 0.22 0505  95  56  -8 0.00
Sat 02/21 23Z 0.25 0606  94  62  -8 0.00
Sun 02/22 00Z 0.27 0707  93  63  -8 0.00
Sun 02/22 01Z 0.28 0808  91  62  -8 0.00
Sun 02/22 02Z 0.27 0908  89  59  -8 0.00
Sun 02/22 03Z 0.27 0909  75  57  -7 0.00
Sun 02/22 04Z 0.28 1111  54  57  -7 0.00
Sun 02/22 05Z 0.27 1213  49  54  -7 0.00
Sun 02/22 06Z 0.25 1316  50  58  -8 0.00
Sun 02/22 07Z 0.22 1417  53  64  -8 0.00
Sun 02/22 08Z 0.18 1417  57  71  -8 0.00
Sun 02/22 09Z 0.17 1416  60  75  -7 0.00
Sun 02/22 10Z 0.16 1415  59  76  -7 0.00
Sun 02/22 11Z 0.15 1414  54  82  -7 0.00
Sun 02/22 12Z 0.13 1414  53  88  -7 0.00
Sun 02/22 13Z 0.15 1414  53  87  -7 0.00
Sun 02/22 14Z 0.18 1315  53  86  -7 0.00
Sun 02/22 15Z 0.21 1315  59  82  -7 0.00
Sun 02/22 16Z 0.25 1215  65  80  -7 0.00
Sun 02/22 17Z 0.29 1215  69  74  -7 0.00
Sun 02/22 18Z 0.31 1215  73  71  -7 0.00
Sun 02/22 19Z 0.34 1215  74  74  -7 0.00
Sun 02/22 20Z 0.37 1214  76  79  -8 0.00
Sun 02/22 21Z 0.38 1214  78  83  -8 0.00
Sun 02/22 22Z 0.37 1214  78  85  -7 0.00
Sun 02/22 23Z 0.41 1116  79  85  -8 0.00
Mon 02/23 00Z 0.46 1017  79  83  -7 0.00
Mon 02/23 01Z 0.52 0919  80  72  -8 0.00
Mon 02/23 02Z 0.56 0921  79  57  -8 0.00
Mon 02/23 03Z 0.63 0924  80  62  -8 0.00
Mon 02/23 04Z 0.61 0924  74  51  -8 0.00
Mon 02/23 05Z 0.59 0823  66  63  -8 0.00
Mon 02/23 06Z 0.60 0825  62  69  -7 0.00
Mon 02/23 07Z 0.55 0723  61  78  -7 0.00
Mon 02/23 08Z 0.54 0724  58  85  -7 0.00
Mon 02/23 09Z 0.55 0625  53  86  -7 0.00
Mon 02/23 10Z 0.61 0628  45  79  -7 0.00
Mon 02/23 11Z 0.65 0632  38  81  -6 0.00
Mon 02/23 12Z 0.66 0633  37  84  -6 0.00
Mon 02/23 13Z 0.69 0534  37  83  -7 0.00
Mon 02/23 14Z 0.68 0531  37  85  -7 0.00
Mon 02/23 15Z 0.66 0528  41  84  -8 0.00
Mon 02/23 16Z 0.68 0427  45  85  -9 0.00
Mon 02/23 17Z 0.63 0327  57  85 -10 0.00

Run total areal avg QPF for the Central_Greens is: 0.12 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